"What is it that nobody tells you about adult life?" originally appeared on Quora--the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Patrick Mathieson, VC @ Toba Capital, on Quora:

General-purpose advice is very different from high-performer advice. Beware of "That one weird trick that Michelle Wie uses to build the perfect golf swing" or "Click here to learn how to invest like Warren Buffett" or "The three exercises that Cristiano Ronaldo uses to maintain his six-pack." Getting from dreadful to average takes a particular set of methods, which are different from those that take you from average to pretty good, from pretty good to great, and so on. Make sure that the advice you're following reflects your stage of proficiency.

All advice from successful people is tainted by survivorship bias. I'm just going to quote the Survivorship bias article on Wikipedia because they say it better than I ever could:

"Whether it be movie stars, or athletes, or musicians, or CEOs of multi-billion-dollar corporations that dropped out of school, popular media often tells the story of the determined individual who pursues their dreams and beats the odds. There is much less focus on the many people that may be similarly skilled and determined but fail to ever find success because of factors beyond their control or other (seemingly) random events. This creates a false public perception that anyone can achieve great things if they have the ability and make the effort. The overwhelming majority of failures are not visible to the public eye, and only those who survive the selective pressures of their competitive environment are seen regularly."

Survivorship bias is just one of a multitude of cognitive biases that needed to be uprooted from our brains if we ever hope to view the world with clear eyes. Speaking of that...

There is no such thing as a completely rational human. Nobody is capable of making decisions that are 100 percent logical and zero percent emotional. It just comes with the territory of being a person. You'll save yourself a lot of stress and angst if you stop expecting people to behave like homo economicus and instead treat them like the emotionally-driven decision-makers that they are.

Most dissatisfaction in relationships (romantic, platonic, familial, etc.) comes from a failure to express one's expectations clearly. Which ties into my next point...

The best way to enforce happy relationships is to exercise your willingness to walk away from them. So many people get bent out of shape because they feel like their employer / boyfriend / best friend / etc. should be treating them a certain way that they aren't. Yet these people never think through what it would actually take for them to end the relationship. Boundaries are meaningless if there's no consequence for violating them. And often people will push and push and push you until they finally reach the resistance point, if ever. To get what you want from your relationships, sometimes you need to exercise that resistance point: "If this is how you're going to treat me, I can't date you / work for you / hang out with you anymore. Sorry."

FOMO is an entirely internal emotional state. Nobody else actually cares if you skip out on that concert or stay in on Friday to eat Ben & Jerry's with your teddy bear. See also: the joy of missing out.

Anything you're trying to accomplish has very likely been performed by thousands or millions or billions of people in the history of humanity, and the vast majority of those people were far less capable and smart and well-resourced than you are. So don't whine about your inability to lose 10 pounds, or play the piano, or ask somebody out on a date, or whatever. You're better than that.

This question originally appeared on Quora--the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google+. More questions: