At some point, not only do returns diminish, but they actually become negative because your productivity during the first forty hours of the week goes down when

At some point, not only do returns diminish, but they actually become negative because your productivity during the first forty hours of the week goes down when you don’t get enough sleep, relaxation, etc. Perhaps that point is at 100 hours/week, or more, but I’d wager that it’s at the 80 hours/week mark where working more decreases your productivity. And yes, it does depend on the activity, but even cold calling customers all day can become too much, or an extra ten hours of calling could make your sixty hours of programming less productive.