I give a lot of lee-way to people when it comes to learning lessons, but this idea that your mind should be on your business 24/7 and nothing else, and that that is somehow healthy... I mean, I don't even know how it's controversial for Josh to say people need to do stuff outside of work.
I am a huge believer that we, as founders, should apply the same standards to ourselves as we do to employees. Enforce personal time and vacations, that sort of thing. If it's healthy for an employee, it's healthy for you, and your business doesn't need one of its founders to burn out.
The artificial "must do everything now right now" rush comes from "Funding will run out!" and "We must be first to market!". Those things will happen either way if you lose one of your founders to burnout along the way. Or even if you don't lose them, your productivity will sink like a horse in wet toilet paper if you don't give yourself limits. Furthermore, "funding will run out if I don't rush" is usually a sign you've taken on funding too early. Give yourself enough time early on.
I'm particularly sensible to all this because I've seen how the games industry has abused employees in the past (and this keeps happening, although less), the same way a lot of founders abuse themselves today. Ridiculous deadlines, trading employee health for "code crunch" as if there's just a lot of ones and zeroes to type until you're done.
Don't pull regular all-nighters, don't order KFC every day because you "don't have time to cook", don't stop reading/gaming/watching TV (that business meeting email can wait until tomorrow). And for god sake, don't neglect your personal life to the point of losing your boyfriend/girlfriend/SO, there's nothing like losing your partner to precipitate burnout.
I've even seen some founders rave about things like the Mythical Man-Month and then stay up 36 hours to "work more on their business", as if sleep wouldn't catch up on them anyway. Dumb, toxic culture.
If you want to create a successful company, there's no room not to do those things. At best you'll burn out. If somehow your company survives, you probably won't like the culture you created.
To be clear: I'm not saying "don't work hard". I'm saying that if you think you can make it by cutting out all personal time, you don't have the stamina you think you do. Almost nobody does, you're not the exception, and even if you are, you're gambling your company with your own life which, in startup lingo, is what we call a "dumb move".
All work and no play makes something something.