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Your 30s are typically a time of deciding what personal relationships mean the most to you.
This transition period, however, can lead to decisions that negatively affect your longterm success.
Those who have already been through that decade say that as their responsibilities increased, it became easier to neglect relationships and ignore opportunities that they would never get again.
We went through the Quora thread "What is the biggest mistake you made in your 30s and what did you learn from it?" and Mark Manson's article "10 Life Lessons to Excel in Your 30s," and collected some of the best responses.
Here are the biggest mistakes people make in their 30s:
They abandon their loftier aspirations.
Twenty-somethings are often willing to settle for a job they're not passionate about, but before they know it, that job turns into their career. An anonymous poster writes that the biggest mistake of their 30s was to become "addicted to a monthly salary," in the sense that they settled for job security over career satisfaction.
If you've ever wanted to start a business or pursue a side project, it will only get more difficult as your responsibilities increase.
They put their career ahead of family and friends.
"Don't just work. Make memories. The older you get, the harder it is to make meaningful relationships. Foster those while you're young," writes Microsoft product designer Michael Dorian Bach, who is now in his late 30s.
They don't let go of negative influences.
Some people start to settle in their 30s because they think taking risks or making bold decisions is for 20-somethings. But age is not an excuse to stay in a relationship, friendship, or job that drains your energy.
"Learn how to say 'no' to people, activities, and obligations that don't bring value to your life," Hayley, 37, tells Manson.
They stop developing themselves.
Even if you spent your 20s collecting degrees, you're doing yourself a huge disservice if you stop learning and growing your interests.
"Most people in their 30s are too busy to worry about self-improvement. But if you're one of the few who continues to educate themselves, evolve their thinking, and take care of their mental and physical health, you will be light-years ahead of the pack by 40," Stan, 48, tells Manson.
They neglect their health.
Bach writes that the pursuit of a career can also be a drain on one's health. "Be healthy. That is priority 1. Don't get into your 30s being slow and tired all the time. It sucks," he says. Develop an exercise routine, and enjoy your mobility while you're still young.
They miss the chance to have kids.
CEO coach Alison Whitmire shares a personal story about how she took getting pregnant for granted in her 30s and chose to pursue a new career opportunity instead of trying to have a child. Years later, after a failed pregnancy and then a failed marriage, she remarried and had a baby at 43. She realizes now that no one is ever adequately prepared to have a child, and if you want one, it's best to do so before it's too late.
They don't spend enough time with their aging parents.
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.
They don't set up a financial foundation for the future.
Altucher writes about the many times in his 30s he bet practically all of his money on a business venture and then lost it. Altucher is doing well now, but he looks back on his failures as the result of recklessness.
As your responsibilities grow, it can seem like what you put into savings won't amount to much come retirement, but it will only become harder to start saving in your 40s and beyond.
They stop having fun.
Just because you're not in your 20s anymore doesn't mean you need to stop 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.