My experience is that people tend to fill the time they give themselves to do things. Give yourself 12 you take 12 hours. But humans have a limit to the focused

My experience is that people tend to fill the time they give themselves to do things. Give yourself 12 you take 12 hours. But humans have a limit to the focused productive work they can do. Lets say it is 4 hours. So of that 12 hr - 4 was really productive and 8 not so much. When I was at my tiredest I often spent hours trying to debug issues that literally took me minutes when I was rested. One time I worked so many hours I lost vision (temporarily) in my eye - called cotton wool spots. I was a generally healthy younger guy. Working this way has health effects. If in fact there is such a thing as 10x engineer - how long do you think you will stay 10X once your health deteriorates. Just my 2 cents.