Isn't it always for your own?
You give something to some else who needs to more then you. You get a good feeling, if you didn't you felt like shit.
You catch a bullet for someone you care about because otherwise you couldn't live with youself anymore.
You get asked a favor. You do it, expecting them to do the same for you.
Etc etc
So at it's core, isn't it all just selfishness really?