Last December, more than 1,000 cus­tomers at a Star­bucks drive-​​thru window in New­ington, Conn., did some­thing irra­tional. They paid for the order of the person behind them in line. The money-​​saving move would be to break the chain: Grate­fully acknowl­edge that the person ahead of you in line paid for your order, then drive off with your wallet firmly in your pocket, cack­ling madly like the Joker.

Why are so many people obeying the unwritten rules of the pay-​​it-​​forward move­ment? (By the way, Pay It For­ward Day this year is April 24—no joke.) The usual expla­na­tion is that fair­ness is a product of altruism, the ten­dency to help other people at a cost to ourselves.

Read the article at Bloomberg Businessweek →