why do good??

why do good? what is our incentive? if i see an old woman crossing the street with a heavy bag why should i help her?? is she going to give me money? no probably not? so why do it? i think the reason we do it is for the good feeling we get after we have helped someone who is in need. that is primary reason that charities can exist, because people want a good feeling when they donate money to people or a cause that needs help. so that makes me wonder... is it selfless then? i dont think so. i think that we always do good because of selfish reasons. if we dont for recognition or fame or a favor in return or money or even that good warm feeling that we get when we do a ''selfless'' good deed. in the end we always do it for ourselves.