Here are some things I really, really wish I knew when I was twenty.

• Love hurts, but not as much as not loving.
• The friendships you nurture will have a greater effect on your life than where you work or what you earn.
• You are not your job. You are not your bankroll. You are not the sum of your possessions.
• The company does not love you. It has no heart. You are replaceable. Keep your parachute handy.
• Few decisions will ever shape your future life more than who you choose to marry. To marry well, you must choose well.
• Love is a commitment.
• Your passions will grow out of your values. Make early, wise choices to value what (and who) is good, trustworthy, and praiseworthy.
• Integrity preserved is honor won.
• Rejoice in your health. It fades fast.
• Find a passion. Pick a hobby, own it: photography, juggling—whatever. Get your 10K hours of perfect practice in early and change your life.[1]
• Don’t bother comparing yourself to others—this only leads to heartbreak, anger, and disappointment.
• Most disappointments arise from unmet expectations. Set realistic expectations for yourself, based on your strengths, then strive to exceed them.
• Don’t drive others to meet expectations they’ve committed to — lead, inspire, and help them do it.
• Don’t set expectations for others when they have not or cannot commit to them.
• Expectations you never communicate and negotiate will rarely be met—except by accident.
• Don’t complain. Either change your situation, learn to cope, or change perspective.
• Don’t worry about getting a big salary in your youth: first learn to execute tasks with skill, excellence, and grace.
• Little stuff matters—even in lowly jobs. The boss notices—and even if not, your peers and colleagues will.
• Ultimately, privacy is a myth: God sees everything. The cloud records everything. NSA files everything. So, live transparently and don't waste useless energy hiding failures.[2]
• Don’t look down on others because they don’t have what you didn’t earn: your intellect, your beauty, and your culture of birth are undeserved gifts. Stay humble.
• Failure is an opportunity: no great man or woman ever achieved significance without great failures. Fail forward.[3]
• Never withhold an apology when it’s merited. Deliver it quickly, sincerely, and personally—before resentment festers.
• You don’t need to nurture old guilt when you’re forgiven. But remembering the shame can help you avoid repeats.
• Mere belief in anything signifies little more than assent: trust and behavior reveal where true convictions lie.
• The main thing you need to do quickly is to stop doing things quickly. Trade hurry for calm, confidence, and precision.
• Everybody needs an editor. Everybody. Especially editors.
• Get your work done first so you can play without guilt. Even better, make work play and the fun never ends!
• If you want to develop your passion and gift, stop worrying about the things you do poorly. Go with your strengths!
• Avoid fights. Seriously. Avoid them like a plague: nobody wins in a fight, even if you walk away unscathed. But when a fight picks you, leave everything on the mat and give it your all. Hold nothing back.
• If you're bored, you’re doing it wrong.
• The skills that will help your career most are the abilities to assimilate, communicate, and persuade. Keep learning.
• Nothing in this life—no pain, no agony, no failure—compares to the eternal joy of Heaven. Live in light of eternity.
• Protect your joy. Nothing is easier to lose by over-thinking, overanalyzing, and second-guessing. On the other hand, always consider the long-term consequences of your choices: stupid decisions made in the moment can rob you of years of joy and happiness.
• Your purpose in life determines how you frame events. You can maintain your joy in the most dire circumstances if you find meaning for your life. Dig deep. (Frankl, Viktor E. Man's Search for Meaning. Boston: Beacon Press, 2006.)
• It truly matters what you think about. Think well by reading good books, building good, loving relationships, having good conversation, and imitating great people.

I'm still learning — in fact I haven’t fully appreciated most of the list I made, myself. And I’m still adding to it. But I’m getting better.

Rich »∵«
http://twitter.com/RichTatum

FOOTNOTES:

1. Gladwell, Malcolm. Outliers: The Story of Success. New York: Little, Brown and Co., 2008.
2. “NSA warrantless surveillance (2001–07).” Wikipedia. Accessed September 24, 2016.
3. Maddock, Mike. “If You Have To Fail — And You Do — Fail Forward.” Forbes. Forbes, Inc., 10 Oct. 2012. Web. 24 Sept. 2016.

UPDATE (09/24/2016): This answer has been flagged as “Needs Attribution” and is, at this date, hidden. I have added an attribution for the notion of 10,000 hours of practice, a link to the Wipiedia article on the NSA, and a reference to Viktor Frankle regarding finding meaning in life, but apart from Googling every statement and finding some sort of third-party claim to back up each assertion, I am at a loss for what to do. (Frankly, I think the citations hurt the article as it makes it seem less like a piece of advice and more like an essay that somebody researched.)

This is a list of “received wisdom.” I should make it clear that I am not inventing anything new here — this is stuff I learned precisely because it was taught to me.

So, unless the articles status is repealed, I expect there will be very few people from this point on who will see this, but for all the people who’ve read this and thanked me, I want to be sure to say, “No, thank you!”

UPDATE (09/25/2016): I was just notified by Quora that my answer and been reviewed and removed from moderation. Thanks!