The CEO of WeWork claims to work almost 20 hours a day in this video (https://www.youtube.com/watch?v=l5tSINazw78). Its impossible to do unless you are spending your time doing light work. Any intensive work that requires brain power will burn you out after 10+ hours. And to do it consistently day in and day out is impossible. I work 7 days a week averaging 10+ hours a day. I can barely hit 18 hours doing straight intensive work, and my day after suffers.