“Welcome to one of the most robust, if troubling, findings from the science of self-control: People who use their willpower seem to run out of it. Smokers who go without a cigarette for twenty-four hours are more likely to binge on ice cream. Drinkers who resist their favorite cocktail become physically weaker on a test of endurance. Perhaps most disturbingly, people who are on a diet are more likely to cheat on their spouse. It’s as if there’s only so much willpower to go around. Once exhausted, you are left defenseless against temptation—or at least disadvantaged.”