In general I agree with you but I am pretty sure there are people who can work at high performance much longer than other people can do. Some people also need only 3 hours of sleep where others need 8 or more. I think it's genetic in the same way some people can run 100 m in 11 seconds without training where others need 14 seconds and will never get even close to 11 even if they train.

If you don't have that "talent" for long work hours it's probably counterproductive to force yourself into something you just can't do.