a good deed—can enhance your endurance by reinforcing your sense of agency: in one study, donating a dollar to charity enabled volunteers to hold up a five-pound weight for 20 percent longer than they otherwise could.14 Worryingly, they gained even more strength from imagining themselves doing an evil deed—confirmation, perhaps, of a theory, long discussed on online running message boards, that the best way to run an 800-meter race is fueled by “pure hate.”15
