Baumeister himself started out as something of a skeptic. But then he observed willpower in the laboratory: how it gives people the strength to persevere, how they lose self-control as their willpower is depleted, how this mental energy is fueled by the glucose in the body’s bloodstream. He and his collaborators discovered that willpower, like a muscle, becomes fatigued from overuse but can also be strengthened over the long term through exercise.
