Many see willpower as something you develop like a muscle, something you can strengthen through practice and mental exercise, but the latest research suggests willpower runs on an internal battery, one that can be drained after heavy use, but recharges after rest and reward. Once you've used it up, you much recharge it or else you'll be unable to keep your hand out of the cookie jar. Speaking of cookies...we also explore in this episode how psychologists have used cookies in novel ways to uncover the secrets of our minds.