Influence: The Psychology of Persuasion

by Robert B. Cialdini

For instance, the model asserts that one of the main motives (goals) of a persuader involves cultivating a positive relationship. Research shows that messages are more likely to be successful if recipients can first be made to feel positively toward the messenger. Three of the seven principles of influence—reciprocation, liking, and unity—seem particularly appropriate to the task.

A well-known principle of human behavior says that when we ask someone to do us a favor, we will be more successful if we provide a reason.