Reciprocity is a strong social norm in most cultures.
People tend to respond to positive actions with positive actions. In other words, when someone does something beneficial for us, we feel inclined to reciprocate and do something beneficial for them in return.
You’ve undoubtedly experienced it. You do someone a small favor. Perhaps you show them where to find some information on line that will help them with a home project. Later, they return your helpful gesture by introducing you to their excellent plumber.
This principle plays a significant role in forming and maintaining social bonds and cooperation.
It also plays a role in building influence. If you are willing to be influenced by someone, they are more likely to be influenced by you.
by Esther Derby