90 hour workweeks come with an undocumented feature, the < 50 years old heart attack.

For a little while, say a couple of weeks it's ok to push yourself like that it if it is actual work, and something you do not enjoy.

If your work is play to you you might get away with it. But anybody that pushes themselves like that is going to find out a few things:

  - there is a price

  - the price includes an interest 

  - your 90 hour workweek is on a per-hour basis not as
    productive as a 50 hour workweek would be

Also, just like in computers, works smarter, not harder.