As Fowler pointed out, if you want to improve the world with your good behavior, math is on your side. For most of us, within three degrees we are connected to more than 1,000 people — all of whom we can theoretically help make healthier, fitter and happier just by our contagious example. “If someone tells you that you can influence 1,000 people,” Fowler said, “it changes your way of seeing the world.”