The expenditure of a finite amount of will. This can result in poor self-control choices.

Baumeister’s group has repeatedly found that an effort of will or self-control is tiring; if you have had to force yourself to do something, you are less willing or less able to exert self-control when the next challenge comes around. The phenomenon has been named ego depletion. - Daniel Kahneman, Thinking, Fast and Slow

One example that comes to mind is that fact that certain folks like Zuck or Jobs would pre-define their wardrobe as a way to avoid ego depletion1.