According to recent research, we have a finite amount of temptation-resistingresources. If we use up all our self-control resisting one temptation, we don'thave any left to use against another temptation.
For example, once we've spentour store of self-control on resisting the temptation to over-eat, we're likelyto have none left to resist the temptation to just sit and watch TV instead ofexercising. And this depletion is corroborated by weakened electrical activityin the part of the brain that lets us know when we're screwing up.
To arrive at their findings, the researchers asked forty college students tosuppress their emotions while watching a distressing movie for ten minutes. Theidea was to exhaust their self-control ration by having them use it all up tofend off their emotions. The participants were then asked to do another taskthat required self-control. The more successful a participant was atsuppressing emotions, the worse he performed on the second task.
An EEG performed during the second task showed weakened activity in the part ofthe brain that tells us when we are off-track; that is, it lights up to let usknow when we are falling off the wagon and failing to exercise self-control. When those neural systems are pooped out, they can't alert us to a mismatchbetween our actions and our goals.
So there we sit in a stupor in front of thetelevision, having virtuously resisted eating all day, with nothing going on inthe part of the brain that is supposed to tell us that we're blowing ourexercise regimen.
Source: Psychological Science, October 2007