Time
Use it wisely.
Enjoy it with others.
Don't spend more of it at work than you have to.
Work and growth matter, but so does a sunset in the mountains. Unless TOPR mountain rescue has to fly in and get you afterwards. Then you'd better stay at work!
Don't fall into the self-employed trap of converting every hour into cash. Some moments are priceless, and you'll only appreciate them some time later.
Go on vacation. Go on a date with a girlfriend or a wife, preferably your own. Spend time with your parents while you still have them. Stare at nature for a while. Enjoy life!
Don't take the failures you rack up along the way personally. Don't treat them as wasted time. Every failure is a step closer to success.
They say an expert is someone who has made all the mistakes that can be made in a very narrow field. Give yourself the time and space to make mistakes, experiment and change direction. Because you only have to win once.
Whenever someone tells me they don't have time, I always reply:
All we have is time
I like thinking about it, because time is the only thing we have, and there comes a time when nothing matters more.