This isn't just for startups. People end up burning themselves out as contractors or even in salaried positions in well established companies, in much the same ways. You think it will work out in the end, but usually it really really doesn't.

"Eyes on the prize" is actually the right attitude, but the prizes should be your sanity, health, and friends & family. Unless you are doing something truly earth shattering like you are close to curing cancer, the world is not going to remember your sacrifice for the cause. I'm close to leaving my nicely paid job in full knowledge that I'll take a hefty pay cut doing so, but the money isn't worth the effect the current environment is having on me, I'm almost done waiting for promised changes to happen, and other changes that are happening may even make things worse (in at least the short term). I am more important than my work. You are more important than your work. If you can manage both then carry on, and it is fine to burn a bit short term to deal with unexpected crisis, but if you find yourself having to chose between the two over the medium/long term then don't chose the work.