The Norm of Reciprocity: Why Gifts Create Debts and Favors Create Obligations

In 1971, Dennis Regan had a confederate give subjects a Coke during a break in an experiment. Later, the confederate asked subjects to buy raffle tickets. Subjects who had received the Coke bought twice as many tickets — even those who said they did not like the confederate. The gift had created an obligation independent of liking, independent of want, independent of the quality of the gift. Reciprocity: the social norm so powerful that Marcel Mauss called it the cement of civilization, and Robert Cialdini called it one of six universal weapons of influence.