Is pushing my limits sustainable?

I was realising that my first startup was failing, and having to accept it. And it's pretty hard when you are the startup, right? Because it is not just accepting that something is not working out or the work is not getting done or we don't get enough investments and stuff like that. It's just that you or the people are not working. So you end up doing two things, you either overwork yourself until you burn out or you end up just drifting away very slowly. For me, it was the first one. And I started overworking and getting too much into it. And after that, I basically burned out. I didn't believe there was burnout. I thought "Oh, I'm into startups. I'm going to work 20 hours a day. That's why I'm here. This is the mindset I have to keep." And it didn't change anything.