Hunter gatherer survivalist genes just kick in.
YMMV, but I consider it a healthy thing for, at least for some part of your career, to work "Amazon hard." Aka, all the reasons that people list when they say you should really try working for a startup.
When you push yourself to your limits at your profession, a lot of stuff clicks into place and you learn so much.
You can't procrastinate, you can't do it wrong, there just isn't the time.