Having worked in software engineering for 17+ years, I've learned a few things (and gone through at least two-bouts of serious burnout). One was at the end of the first dot-com boom when getting engineering jobs was nearly impossible, so it was a forced long-term vacation. I went to Europe for a bit.
1) In my 20s, I worked all the time. Didn't live a very balanced life, this lead to burnout, especially if you're working in a startup environment where you think you'll retire at 30.
2) I quit engineering twice (but after 6+ months off, new developments in technology that stimulated my imagination eventually brought me back)
3) I've learned to manage not working the burn-out dream, that likely in the long run, your 80 hours weeks aren't going to pay out. It's proven to me that there's plenty of successful people and companies who work realistic hours.
4) Hobbies. I prefer those where I get excercise (like cylcing). Gives me time to clear my mind and keep my body fit and invigorated. I also enjoy gourmet cooking.
5) Managing workload, prioritizing things that are important and recognizing things that you think are work but really procrastinating.
6) Learn other professional skills than typing text into your favorite editor/ide. Speaking at conferences/local user groups, managing project budget, managing teams, managing bigger teams. Doing these other things makes you appreciate the few hours of coding you have left in the week.