Reciprocity

Reciprocity is a social norm in which people respond to an action with an equivalent action. This may be a positive or negative action. The idea of reciprocity has led to many other discoveries of human behavior, such as the door in the face technique, whereby a person makes an initial large request, knowing that it will likely be declined, only to make a smaller request that the responder will feel obligated to agree to in order to 'return the favor'.