Help an elderly woman cross the street? Selfish. Give away all of your money to charity? Selfish. Take a bullet for someone else? Selfish. 

Every little thing you do is driven by selfish reasons; you do it because you enjoy it.

What you enjoy, whether it be helping or hurting, is largely determined by your upbringing. Those who enjoy helping others enjoy it because of the positivity they have associated with those types of actions, most likely because of their parents and their friends around them.

The sooner you realize and make use of this information, the better.