Hindsight is 20/20, as they say, and it can often lead to regret.

Some people have the philosophy that everything happens for a reason, and there is no point in having regrets.

But for many of us, looking back on our lives can lead to lingering on one poignant moment or period when we wish we had done things differently That nagging question, "What if ...?," plays on repeat in our heads.

"This may sound a little melodramatic, but no matter how happy you are, at my age your regrets are countless," writes Quora user Gary Teal. "You have made decades' worth of little miscalculations you can't completely erase from your memory, as well as a number of big mistakes that made life permanently harder."

Vaughn Bell at Mind Hacks notes that there are two ways people frame their regrets: The things they did that they wish they hadn't, and the things they wish they had done but didn't.

"The difference between the two is often a psychological one, because we can frame the same regret either way — as regret about an action: 'If only I had not dropped out of school;' or as a regret about an inaction: 'If only I had stayed in school.'

"Despite the fact that they are practically equivalent, regrets framed as laments about actions were more common and more intense than regrets about inactions, although inaction regrets tended to be longer lasting," Bell writes.

Quora user Bradley Voytek points to a national survey about the regrets of a typical American, which found 13 common sources for regret. They are, in order: romance, family, education, career, finance, parenting, health, "other," friends, spirituality, community, leisure, and self.

Here are some of the most common regrets as chronicled by Quora users (answers have been edited for clarity): 

SEE ALSO: 17 bad habits you should break in 2017 to be more productive

DON'T MISS: 18 highly successful people share their New Year's resolutions

Romance

"I regret that I never fell in love with someone who was in love with me, when that would have been easy for me to do.

"I regret being like an old song sung by Buffy Sainte-Marie: 'Must I go bound and you so free, Must I love one who doesn't love me, Must I be born with so little art, As to love the one who would break my heart?'" —David Kahana

Family — Children

"For as long as I can remember, I have wanted to have kids. But in my younger years, I foolishly assumed that unlike certain accomplishments like a career, the marriage and kids thing would just happen.

"Well, they didn't. I dated plenty of people but never even thought about making family a priority. Then, in my late 30s, a bout with ovarian cancer left me permanently infertile.

"I think about the kids I never had every day, several times a day. I have a great relationship with my nieces and nephews, and volunteer at a children's hospital on a regular basis, but it's just not the same to be around other people's kids. I would love to adopt or be a foster mother, and hopefully be in a financial and domestic situation that would make this feasible one day.

"But again, not the same. And it pisses me off when people say, "You're lucky you don't have kids, they're so much work, blah blah blah." Yes, but a lot of things in life that are worthwhile are also so much work.

"I think the mothering instinct is so strong in some women that the knowledge that one will never get a chance to give birth and raise their own child goes beyond regret. One that a bar chart cannot capture. I can deal with most of my other regrets in life but am having a hard time dealing with this one." — Caroline Zelonka

Family — Parents

"I regret not choosing to spend more time with my parents in my 20s. I lost my mother in 2000, and I feel the loss of the friendship we never had.

"She was very demanding, very strict, and from the perspective of a young man, very unreasonable. It turned out, as I live through middle age, that most of the ideals I have today ended up being the ones she put on me.

"Sometimes, after a setback, I feel the impulse to call her, and in the second or so that it takes for me to realize she isn't alive to speak to any longer, I realize how much I still need her.

"You cannot negotiate with death. It is final, often sudden, and personal. The last night I had with her, at a hospice in Chicago, I was exhausted and asked her if she minded if I went home. She immediately whispered that absolutely, I should rest, and to be careful driving home. I curled her fingers around the nurses call button, and kissed her on the forehead. I remember I felt some relief that I was leaving.

"I know it didn't make a difference, leaving at that time, or leaving a few hours later. She was going to die either way. But reflecting on that moment today I know then that I didn't understand how precious those minutes were, and how a door was being closed that would never open again." — Jim Wagner

My gym membership costs $90 a month.

I know.

Really — I know.

Yes, I have tried to negotiate, and yes, I've looked into other gyms, but after joining my Manhattan chain on a corporate discount that was about $20 less than I currently pay, I couldn't bear to leave the gym when I went back to civilian status after changing jobs. I love the teachers! I know the schedule! The locations are so convenient!

That's how they get you.

Anyway, the price of my gym is what it is, and I paid for a year in advance just to get that rate. So I better make it worth my money. Every night that I "don't feel like going" means I'm wasting cash, and as someone who would be naturally well suited to those hover chairs from Wall-E, there are lots of nights I need to turn "don't feel like" into "can't wait."

How do I force myself to go? Below, I'm confessing the motivation tricks that get me off the couch and onto the spin bike. I can't guarantee they'll work for you — I can't even guarantee they'll continue to work for me — but this is what works right now.

SEE ALSO: I just ran my first half marathon — here's what I tell my friends when they say they could never start running

I leave my gym bag at the office.

This is decidedly trickier if you're the type to work out before and after work, but I haven't yet reached that level of lunacy. As someone who exclusively exercises at night, I bring my gym bag home, empty it, refill it, and bring it to work the next day, whether I'm planning to go to the gym or not.

On the weekend, I just bring it home and then back on Monday morning. This way, I'm never caught without sneakers … and I get an arm workout during my commute.

I think of the money.

The brilliant thing about belonging to a gym, as opposed to those $35 boutique spin classes so many of my friends adore, is that since you've already paid, it gets cheaper every time you go.

That's amazing! If I go to one class in a month, it's a $90 class. Two, they're each $45. Nine classes? At nine, which works out to fewer than three times a week, I'm paying only $10 per class.

I ask my office gym buddies if they're going ... every day.

Because you can't ask and then go, "Oh, just wondering. I will not be joining you. I have some important Netflix to watch."

Schrödinger's got nothing on a good cardboard box. Author of "The Lion in the Living Room," Abigail Tucker, takes us into the feline mind, explains exactly what the puss is up to when inside of boxes, and why we find Maru so watchable.

Follow Tech Insider: On Facebook

Join the conversation about this story »

Architecture firm LAAB transformed this 309-square-foot Hong Kong apartment. Using smart technology, the team was able to build a luxury apartment with many convertible spaces.

Follow BI Video: On Twitter

Join the conversation about this story »

While President-elect Trump spends the holidays at Mar-a-Lago, his expansive Florida resort, we took a look at some of the western ranches and New England compounds past presidents have called home away from the White House.

Follow BI Video: On Twitter

Join the conversation about this story »

The founder of Lammily, Nickolay Lamm, who introduced realistically proportioned dolls to the market, created these images of idealistic body shapes of men throughout American history.

Follow Tech Insider: On Facebook

Join the conversation about this story »

GreenRush is one of several California startups providing a legal weed-delivery service. Partnering with hundreds of dispensaries in the state, the San Francisco-based company provides door-to-door service of your cannabis, edibles, oils and more.

Follow BI Video: On Twitter

Join the conversation about this story »

There are so many diets out there, but figuring out which one will actually work for you can be tough.

Luckily, scientists have found that most reasonable diets can help you lose weight, compared to not following a diet at all. Overall, studies have shown that diets rich in plants and low in processed foods are the best for weight loss.

But many popular diets aren't based on sound scientific principles.

If you're setting a New Year's resolution to lose weight in 2017, here's what the science says about 15 popular diets, so you can decide which one — if any — might be right for you.

SEE ALSO: You lose a bunch of weight every day — here's where it all goes

DON'T MISS: 17 scientific facts to motivate you to eat healthy even when you really don't want to

What you do: The South Beach diet is a three-phase program designed by cardiologist Arthur Agatston in 2003. In the first phase, you cut out all carbs, fruits, and alcohol. In phases two and three, you gradually add some of those foods back in (as far as carbs go, you're only supposed to eat whole-grain ones). It's important to note that this is a commercial diet, so you may have to buy the official plan and materials.

What the science says: The diet focuses on whole foods, which is good since studies have shown this is the best approach for weight loss. Cutting out any of the food groups could leave you lacking nutrients, though. Some people on the diet have reported ketoacidosis, a condition with symptoms including bad breath, dry mouth, tiredness, dizziness, insomnia, nausea, and constipation. Studies have found South Beach diets (or those very similar to the name-brand version) could help people lose weight in the short-term, but researchers haven't followed people long-term to see if it helps them keep the weight off. The problem here is that while the second two phases of the diet are somewhat reasonable, the first phase is very restrictive, so some people might have trouble sticking to it.

What you do: On the new Weight Watchers (the one Oprah has advertised lets you eat bread), their SmartPoints program assigns foods points based on their nutritional values. You get a set number of points per day depending on your height, weight, gender, age, activity level, and how many pounds you want to lose. The plan can cost between about $20 and $70 a month, depending on whether you pay for add-ons like coaching or meetings.

What the science says: Research has overwhelmingly positive conclusions about Weight Watchers' sensible rules, and the new program is even more in line with what nutritionists recommend. Participants in a clinical trial on the plan for a year lost nearly 7 pounds. And other studies have found Weight Watchers members also tend to lower their heart disease risk and blood pressure. An interesting analysis found that participants on Weight Watchers for a year typically paid $70 per pound lost, but gained $54,130 in quality of life improvement.

What you do: There are many different kinds of vegetarians, but generally, you don't eat meat or fish.

What the science says: In observational studies, vegetarians tend to weigh less than their carnivorous counterparts. Cutting meat from your diet could reduce your environmental impact as well, research has found. You have to make sure you get enough nutrients (especially protein) from other sources like nuts, grains, and dairy, though. But the benefits could be considerable: Studies have found that vegetarianism is linked with lower chances of heart disease and cancers, and higher chances of living longer.

The American Dream has transformed over time.

To find out what it means to Americans today, personal-budgeting company You Need A Budget and market-research company OnePoll surveyed the financial aspirations of 2,000 Americans.

The result is a list of 30-plus signs that indicate achievement of the modern American Dream, ranging from paying for a Netflix account to shopping at Whole Foods to owning a second home.

Below, find 16 signs from the survey that you've "made it." And remember: Just like the Dream has evolved over time, it also varies from person to person. Whether or not you've truly "made it" isn't about your car or travel schedule. It's completely up to you.

SEE ALSO: The 25 most expensive ZIP codes in America

DON'T MISS: How much money you need to save each day to become a millionaire by age 65

You own property valued between $1 million and $2 million.

Homeownership in the US fell to a multi-decade low in July 2016. Less than 63% of Americans owned a home, potentially in part due to millennials prioritizing paying significant loans for their education over buying property.

Among those who do own a home, many don't know how its value changes over time, according to a 2015 Zillow survey. If seven-figure property signifies the American Dream to you, make sure you know what your home is worth (and what could trash its value).

You have $7,425 in your checking account.

Surveyed Americans said maintaining $7,425 in their checking account was a sign of success.

According to certified financial planner Sophia Bera, the right amount to keep in your checking really depends on how much you make.

"A good rule of thumb is to keep at least one month of net pay in your checking at all times. Look for a checking account with no monthly fee and no minimum balance. Even better, find an account that reimburses ATM fees from other banks," Bera wrote on Business Insider, adding that it's smart to keep your checking and savings at different banks to avoid the temptation to dip into one or the other.

You go on at least two annual trips abroad.

While Americans collectively leave hundreds of millions of vacation days on the table every year, survey participants agreed that embarking on at least two trips abroad annually is a sign of achieving the American Dream.

And increasingly, they want those vacations to have value.

An American Express Travel survey of US adults earning $100,000 or more revealed that 81% of Americans are seeking deeper and more personalized experiences abroad, while 73% "said they would be willing to exceed their budget to have a unique local experience when they travel, and more than half said they would splurge to enjoy the cuisine of a particular destination."

Research has shown that certain conversation topics have a higher likelihood of leading to a second date.

Follow BI Video: On Twitter

Join the conversation about this story »

At $1.3 trillion, student-loan debt in the US exceeds car loans and even credit-card debt. But education is an investment for the future, or so the mantra goes. Students routinely pay hefty costs to come away with the diplomas they desire.

With that in mind, Business Insider rounded up some of the most costly degree programs around the world.

The programs span some of the expected categories, like medical degrees and MBAs, to less likely bachelor of arts programs and music degrees.

The prices listed below reference only tuition costs without room and board and other expenses.

Below are seven of the most expensive programs in the world:

SEE ALSO: The top 15 American cities for young college grads

Wharton School — $192,900 Executive MBA

Wharton School of the University of Pennsylvania has a two-year executive-education program that runs students $192,900.

Known as one of the top business programs in the world, Wharton grads have an average base salary of $127,280 upon graduating.

Sarah Lawrence College — $204,784 Bachelor of Arts

Sarah Lawrence, based in Westchester County, New York, costs students $204,784 for four years. 

The liberal-arts school has a unique and individualized approach to learning where there are no required courses and examinations mostly don't exist.

Harvey Mudd College — $209,532 Bachelor of Science

Harvey Mudd appears to be one of the most expensive undergraduate program in the US. The Claremont, California-based program runs students $209,532 for four years.

It focuses on science, mathematics, and engineering, and graduates earn an early-career average salary of $78,200 and $133,000 mid-career.

Harvard psychologist Amy Cuddy, author of "Presence," talks about the best way to fake it till you make it in life.

Follow BI Video: On Facebook

Join the conversation about this story »

Follow BI Video: On Twitter 

Join the conversation about this story »

Shake Shack founder and CEO of Union Square Hospitality Group, Danny Meyer, started his first restaurant at 27. He looks back at the biggest mistake he made in the early years of his career as a restaurateur.

Follow BI Video: On Twitter 

Join the conversation about this story »

Whether it's nuclear warfare or a zombie apocalypse that triggers the end of the world, Vivos Group wants you to be prepared. The California-based company builds and maintains massive fortified shelters where high-net-worth families can buy space and live out Armageddon.

Its new development, Vivos xPoint, is billed as the largest private shelter community on Earth. The bunker community houses up to 5,000 people and can withstand a 500,000-pound blast.

Take a look inside this modern-day Noah's Ark.

SEE ALSO: A tech exec just bought the penthouse in San Francisco's sinking skyscraper for $13 million

"This is the place you will want to be when the SHTF," or s--t hits the fan, according to a release from Vivos Group. No one calls xPoint home just yet.

The property contains 575 bunkers made of hardened concrete and steel.

Located in South Dakota, the structures were originally built by the Army Corps of Engineers in 1942 as a military fortress that stored explosives and munitions.

The bunkers were built to withstand a 500,000-pound blast from explosives within.

When it comes to your daily hygiene routine — from your flossing habits to your nightly shower — you might think you've got everything down pat.

But we're here to shake things up.

Heeding advice from medical associations and professionals, we compiled the optimal ways to keep yourself clean, healthy. and looking sharp.

SEE ALSO: Why you should never use alcohol to help you fall asleep, according to science

DON'T MISS: Which body part hurts the most when stung by a bee? A scientist put himself through a torturous experiment to find out

1. How often should I wash my hair?

The short answer? Nobody needs to wash their hair everyday. Beyond that, it depends on your skin type: if you have normal or dry skin, once or twice a week should do the trick.

2. How often should I brush my teeth?

The American Dental Association recommends you brush twice a day for two minutes, although they don’t specify what time of day these brushing should happen. So long as you do a good brushing before bed, you should be set. While you sleep, your mouth salivates less, which can lead to cavities.

3. When's the best time to put on antiperspirant or deodorant?

The ideal time is right before you go to sleep. That way, if you’re using an antiperspirant, it has time to close your armpit’s sweat ducts before they have a chance to get sweating in the morning. Most last at least 24 hours, so no worries about not making it to the end of the workday.

If you pay close attention to Business Insider's Strategy vertical, you'll notice we frequently share productivity tips from an expert we've just interviewed, a book we've just read, or new research we've just scoured.

And we admit it can be a little daunting to keep up with all the advice out there.

So since you're here to learn how to make better use of your time, we thought we'd save you some and round up the best productivity tricks.

To do this, we asked some of the experts we trust to share how they get it all done.

Here's their favorite productivity advice:

SEE ALSO: 18 bad habits you should break in 2017 to be more productive

DON'T MISS: 11 TED talks that can help you become insanely productive

Associate something you love with something you want to accomplish.

"Pick a ritual that you love — for me this ritual is the morning coffee — and connect it to a productivity-related activity. In my case, it has to do with writing.

"So I connect something I love, which is the coffee ritual, to something else that I love in principle, but not every moment of it, which is writing. It's an almost conditioned response, where I start working and I'm enjoying the coffee and the writing at the same time."

— Dan Ariely, a professor of psychology and behavioral economics at Duke and author of "Payoff"

Be more compassionate.

"My top productivity tip? Compassion. Wait, what? Aren't productivity tips typically about shifting mindset, single tasking, deep focus, working in pulses, and a host of other useful tools? Yes. And all those tools can help us be fantastically productive, effective, and even more creative.

"But what compassion recognizes is that we're human. We're going to have stupid days, when nothing seems to go right. We just will. There will be times when we're going to be distracted, unmotivated, scattered, when some crisis at work or in life kept us up all night, or when we're feeling just plain overwhelmed.

"But rather than beat ourselves up, sink into paralyzing negativity, or ruminate endlessly on what went wrong or how we failed, compassion enables us to forgive ourselves, to learn what we can, to see that it's all about practicing, to let go of perfection, and — lightly and with grace — move forward and try again."

— Brigid Schulte, author of "Overwhelmed: Work, Love, and Play When No One Has the Time" and director of the Good Life Initiative/Better Life Lab at New America

Make accomplishing your task a necessity.

"A key to maximizing productivity is to forget about what you already know — or think you know — about motivation. We typically assume that there's a direct correlation between how much we want to achieve a given outcome and how likely we are to actually achieve it.

"However, there's a much more constructive way to think about motivation — that's to think of it as something you must custom manufacture for each and every goal you wish to achieve. By custom manufacture, I mean to deliberately and creatively put yourself in situations that make you urgently feel like it's necessary.

"Here's my favorite example: After failing time and time again to stick with his good intention to exercise daily, Joe custom manufactured a situation that changed everything. He simply agreed to, from now on, own only one stick of underarm deodorant and keep that one stick of deodorant in his locker at the gym. So the only way he could spare himself from the mortifying embarrassment of stinking all day was to go to the gym. Once he was there, he would feel too foolish about just using his deodorant and leaving, so he would stay and exercise. Joe essentially tricked himself into doing what he intended to do, and eventually exercising daily became a self-sustaining habit."

— Steve Levinson, clinical psychologist and author of "The Power to Get Things Done"

Stanford University's acceptance rate hit an all-time low for the class of 2020, with 4.69% of applicants accepted into the prestigious California-based school.

That means Stanford is the most selective college in the US, beating out all Ivy League institutions.

But while getting into Stanford might seem like a nearly impossible task, many other achievements in life — like acceptance into some elementary schools — are more difficult than earning a spot within the school's prestigious walls.

Ben Winsor and Christina Sterbenz also contributed to this story.

SEE ALSO: Early acceptance rates to Ivy League schools are drastically higher than regular — but the reason why isn't as obvious as it seems

A spot at one of New York City's top elementary schools

The elementary admissions process in New York City is utterly grueling. Among exemplary schools, one stands out as the gold-standard:Hunter College Elementary School.

Each year, Hunter chooses 25 girls and 25 boys from all of Manhattan to be admitted to its incoming kindergarten class.

They're hand-selected from a pool of about 2,500 applicants, according to the website Inside Schools. That makes the acceptance rate for Hunter 2%. 

A job as an NBC page

Landing an internship-like role in the National Broadcasting Company's page program is competitive to say the least. Famously, the character Kenneth Parcel was a page on 30 Rock.

For example, in 2016 there were 2,600 applicants for 120 positions, for a 4.6% acceptance rate.

The NBC page role is a year-long entry-level role where employees perform PR responsibilities among other tasks depending on their department.

A spot at an innovative startup college

College startup Minerva Schools has received 16,000 applications for 306 available places this year, the Financial Times reported.

Its model vastly differs from four years of school at other prestigious colleges. Students don't stay in one place during their four-year education.

They spend time in up to seven residence houses in San Francisco, California; Berlin, Germany; Buenos Aires, Argentina; Seoul, South Korea; Bangalore, India; Istanbul, Turkey; and London, England.

At 1.9%, the acceptance rate for the unconventional college is far lower than at Stanford.

The citizens of this 240-acre "communist utopia" are very wealthy but aren't allowed to speak to the press.

Follow BI Video: On Twitter 

Join the conversation about this story »

For many people, the summer months symbolize pleasure reading at its best.

It's a time to indulge in the texts that are most appealing, without scrutiny: an easy beach read, a guilty pleasure, or that book you've always meant to start.

But students at America's most prestigious private schools must still endure the rigors of homework during their summer vacations with a little reading — some required, some merely recommended. The titles cover issues such as war, sexuality, and racial history.

Check out the books current seniors at prestigious private schools across the US added to their libraries:

SEE ALSO: 14 things that are harder to get into than Stanford

The Hotchkiss School — Lakeville, Connecticut

Students must read three books of their choosing plus the required items below:

Read (novel) — "The Things They Carried," by Tim O'Brien

Read (novel) — "The Absolutely True Diary of a Part-Time Indian," by Sherman Alexie

Watch — "The Hunger Games" (2012)

Read (poem) — "A Work of Artifice," by Marge Piercy

Trinity School — New York, New York

Students can choose to read one or more of the books on the list below and then participate in informal discussion groups in the fall:

"Alice in Wonderland," by Lewis Carroll

"All the Light We Cannot See," by Anthony Doerr

"The Boys in the Boat," by Daniel James Brown

"Catch-22," by Joseph Heller

"Closely Watched Trains," by Bohumil Hrabal

"Color of Magic," by Terry Pratchett

"Crime and Punishment," by Fyodor Dostoevsky

"Deep," by James Nestor

"The Martian," by Andy Weir

"The Old Man and the Sea," Ernest Hemingway

"The Wind in the Willows," Kenneth Grahame

Deerfield Academy — Deerfield, Massachusetts

Students must read four books that they choose from a list of over 50. Titles on the list include:

"Half of a Yellow Sun," by Chimamanda Ngozi Adichie

"The Circle," by Dave Eggers 

"A Clockwork Orange," by Anthony Burgess

"The Universe and The Teacup: The Mathematics of Truth and Beauty," by K.C. Cole

"Invisible Man," by Ralph Ellison

"Madame Bovary," by Gustave Flaubert

"To The Lighthouse," by Virginia Woolf