Your 30s are typically a time for settling down after using your 20s to take risks and find yourself.
Many 30-somethings are busy rising through their work hierarchy, developing a serious romantic relationship, and possibly raising a family.
Those who have already been through that decade say that as their responsibilities accumulated, it became easier to neglect relationships and ignore opportunities that they would never get again.
Quora users discussed lessons they learned in the thread: "What is the biggest mistake you made in your 30s and what did you learn from it?"
We've collected some of the most insightful responses.
You aren't driven by purpose.
"Success" doesn't have to be equated with wealth and prestige.
It's common for undergraduate college students lacking specific career goals to pick a relatively safe, well-tread path with the hope that things work out. At some point in their 30s, some of these same people may have multiple degrees and wealth but realize that they are deriving no meaning from their career.
This happened to designer Jack Sheu when he was 35. "I learned that if you don't have your purpose, then make it your obsession in life to find it," he writes. "It took me over a year, and I was completely disconnected from the rat race during that time. Don't stop until you've got it. You'll know when you have."
You don't set up a financial foundation for the future.
If you developed a spending habit in your 20s at the expense of saving for your future, it's not too late.
An anonymous poster wrote that when his salary increased dramatically, he started spending excessively on things like expensive cars, a motorcycle, and a boat. Only in retrospect did he realize the danger of burning through money.
"Had I invested the money instead, I could have comfortably retired now (I am 44)," he writes.
You neglect your personal relationships.
You'll likely spend your 30s in a senior position that requires significantly more time and energy than your job did in your 20s. For the sake of your well-being, you should be vigilant about scheduling time specifically for your family and friends. The fulfillment you can gain from keeping loved ones close will keep you happier and more productive.
"Don't just work," writes Microsoft product designer Michael Dorian Bach, who is now in his late 30s. "Make memories. The older you get, the harder it is to make meaningful relationships. Foster those while you're young."
You don't spend enough time with your aging parents.
Don't forget about the people who raised you.
Entrepreneur and blogger James Altucher, who is now 46, writes about a particularly difficult memory for him: "When I was 34 I hung up the phone on my dad in an argument and never returned his calls. Six months later he had a stroke and died. A week before that he had emailed me to say hello but I didn't return the email. I'm sorry, Dad."
It can be easy to forget that your parents grow older as you do. Don't take them for granted.
You neglect your health.
Your body won't be able to handle when it could when you were younger.
Bach writes that the pursuit of a career can also be a drain on one's health. "Be healthy. That is priority No. 1. Don't get into your 30s being slow and tired all the time. It sucks," he says.
Do what you can to stay healthy: Exercise, eat right, limit your vices, and take care of your mental health.
You think you have to be completely 'ready' to start a family.
There is not, of course, a correct time to have a child. But one of the most recurrent regrets among people writing in the Quora thread was waiting too long to start a family. Regardless of family structure, they agreed that your 30s are a good time to make a decision if you want to raise kids or not.
CEO coach Alison Whitmire, now 44, writes that only after she became a mother did she realize that her fear of not being ready to have a child was unfounded, since no one is ever adequately prepared to have one for the first time.
They stop having fun.
Don't forget what actually matters.
Just because you're not in your 20s anymore doesn't mean you need to give up enjoying life. Bach says he spent the early half of his adult life chasing money, and it only made him unhappy and more cynical about life.
Go on dates with your significant other. Take your kids on trips. Go to concerts with your best friends. Just don't forget that the money you work to make is useless if you're miserable.