“If you take antidepressants and they make you better, the psychological attribution is external,” he says. “Patients believe that the reason they get better is because of the drug they take. People believe, ‘I cannot even function without having to rely on this external thing that helps me get through the day.’ “With exercise,” he says, “the attribution is internal: ‘The reason I get better is because I myself try. It’s not that somebody else is giving me a pill, it’s that I am putting in the effort.”