Self Control is a Limited Resource...

Use it wisely (New York Times). This may actually explain a lot:

The brain has a limited capacity for self-regulation, so exerting willpower in one area often leads to backsliding in others. The good news, however, is that practice increases willpower capacity, so that in the long run, buying less now may improve our ability to achieve future goals — like losing those 10 pounds we gained when we weren’t out shopping. The brain’s store of willpower is depleted when people control their thoughts, feelings or impulses, or when they modify their behavior in pursuit of goals.

Update: Additional (and practical) thoughts here.