Dan Ariely Blog Archive Understanding Ego Depletio:
Eventually, when we’ve said “no” to enough yummy food, drinks, potential purchases, and forced ourselves to do enough unwanted chores, we find ourselves in a state called ego-depletion, where we don’t have any more energy to make good decisions. So–back to our earlier question–when you contemplate your Friday versus Sunday night selves, which one is more depleted? Obviously, the former.
You may call this condition by other names (stressed, exhausted, worn out, etc.) but depletion is the psychological sum of these feelings, of all the decisions you made that led to that moment. The decision to get up early instead of sleeping in, the decision to skip pastries every day on the way to work, the decision to stay at the office late to finish a project instead of leaving it for the next day (even though the boss was gone!), the decision not to skip the gym on the way home, and so on, and so forth. Because when you think about it, you’re not actually too tired to choose something healthy for dinner (after all, you can just as easily order soup and sautéed greens instead of beef lo mein and an order of fried gyoza), you’re simply out of will power to make that decision.