Just One _____ .

I recommend this article on Salon.com about why it's so difficult for us to control our appetites and our actions.
The reason diets don't work, according to the author of a new best-selling book on the matter, is not that the body returns to a certain set point — it's that the brain does:

"In people who have a hard time controlling their eating, their brain circuits remain elevated and activated until all the food is gone. Then the next time you get cued, you do it again. Every time you engage in this cycle you strengthen the neural circuits. The anticipation gets strengthened. It's in part because of ambivalence. Do you ever have an internal dialogue? 'Boy, that would taste great. No, I shouldn't have it. I really want that. And I shouldn't do it.'

That sort of ambivalence increases the reward value of the food. It increases the anxiety, it increases the arousal, it keeps it in working memory. We're wired to focus on the most salient stimuli in our environment. For some people it could be alcohol or illegal drugs or nicotine or sex or gambling. For many of us it's food."