Originally Posted by cutedimples

In Psychology, it's called the Ben Franklin effect. When you do someone a favor, it's more likely that you'll do that same person another favor than he/she will return the favor. Likewise, if you hurt somebody, it's more likely that you'll hurt that person again than he/she will hurt you back.

I think we are highly adaptive in order to survive. Little kids always know who to throw a temper tantrum to. Even my little pup knows who spoil him and who not.