As a founder, it appears as if our startup's success or failure depends on us cofounders. This drives me to work insane hours as some sort of ego self rationalization tells me that more work will make it succeed.

In general I have seen the work/result correlation hold true. And yet, we all know how luck plays its role. I personally like to think some events are meant to happen or not. Especially when it goes bad - when my startup lost a client in the early days for example it was extremely tough... but we learned so much that the next bigger one went well. Would working more hours have changed anything, I doubt it, so there is more to it than work.

More than this, working many hours is sometimes just a way to reduce anxiety of success or failure, at least for me. What's tricky is understanding which hours not to do, how to make more of the ones I do, and being confident that cutting the hours won't affect the bigger picture output too much. Easier said than done.