I'm not sure that's true. It certainly isn't in my case. Most of the successful startups I've been around actually have done quite the opposite (including my own.. I'm comfortable calling us "successful" now).

While there are periods of insanity, the overall cadence of a successful startup (again in my experience) trends towards sanity. Very people in the world have the mental endurance to keep a super intense level up for a long period of time. The founders who recognize that (again, in my experience) tend to have better outcomes.

One thing to note: there is a curious thing about startup founders. I've always found it interesting that when they draw up the narrative of their startups path they tend to emphasize those long periods of work while minimizing the (more common) periods of relative calm. As an outsider you think everyone is working 80-100 hour weeks. From their stories, you'd believe it too. The reality doesn't always match the narrative tho. Just ask the social network.