Fascinating article from The Wall Street Journal:
Willpower, like a bicep, can only exert itself so long before it gives out; it’s an extremely limited mental resource.
Be sure to read the whole thing.
What’s interesting is how many factors impact willpower. Mental exertion, not getting enough nutrition, and even slouching all adversely impact your ability to resist temptation. So take a break, eat often, and sit up straight.