|The six element of persuasion from the element ASSCURL is Reciprocation.|
Reciprocation is the act of returning a favor to someone. It is my belief that everyone acts for the own reward. No behavior is done without a benefit to the giving.
Some examples of reciprocation are:
Almost anything that's free should alert you to the reciprocation effect.
There is a human bias to reciprocate favors when one is done for you.
Note that Reciprocation can be negative. If you behave a certain way that's perceived as negative then someone may do a negative to you.
If you fail to reciprocate this can make people angry at you.
Do some research on Cialdini's Reciprocation.