“There are way easier places to work, but nobody ever changed the world on 40 hours a week,” he said in a tweet, after saying SpaceX, Tesla (IW 500/99), Boring Company and Neuralink are the places to be if “getting things done matters to you.”Tesla’s CEO Elon Musk says he knows how many hours a week you need to work to change the world, and it’s no small number.

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When asked by a user exactly how many hours one had to work a week to change the world, he said 80 was a sustainable number, with peaks above 100 at times.

“Pain level increases exponentially above 80,” he warned.

The comments came just a day after the airing of an Axios interview with Musk on HBO in which he said Tesla came just weeks from financial ruin during its frantic and costly effort to ramp up production of the Model 3 sedan.

“The company was bleeding money like crazy, and if we didn’t solve these problems in a very short period of time, we would die,” Musk, who has been known to sometimes sleep at his factory, said in the interview.

By Nathan Crooks