I started to think of the three elements of luck as being like one of those old-fashioned slot machines where you pull the handle and three items have to line up in a row. People get addicted to waiting for the three cherries, for example, to appear next to one another. Psychologists call it “variable ratio reinforcement”—you don’t know when you’ll get the reward, so you keep trying, expecting it to appear at the next pull of the handle.