Cialdini describes a professor sending Christmas cards to total strangers. Many of these strangers sent cards in return. Cialdini terms this lever of influence “reciprocation.” People throughout history have found it important to respond to generosity with generosity. He quotes anthropologist Richard Leakey, who says that this type of reciprocal sharing is a pre-historical act of survival. Cialdini also points out that the British Magna Carta enshrines reciprocation: When dealing with an opposing enemy, one must treat civilians as the enemy treats British civilians.

In “How the Rule Works,” Cialdini details the competitive advantage reciprocity gives those who know how to use it. He says, “The rule possesses awesome strength, often producing a yes response to a request that, except for an existing feeling of indebtedness, would have surely been refused” (29). Cialdini notes that one does not have to like the person requesting the favor before feeling the need to respond positively. Cialdini describes the impact of reciprocation in the business world, where McDonald’s managers learn that they sell more food when they give balloons to children upon arrival rather than upon departure.

Cialdini notes the significant impact of reciprocation upon politicians. The rule of reciprocity, he says in “Politics,” causes politicians to turn their backs on constituents and parties in order to return favors bestowed upon them.