The high school kid who volunteers at a homeless shelter and hopes it will help their college app is likely doing it both out of altruism and self-interest.
(Actually, the person who helps people because it feels good is also acting out of self-interest).
Given many ways to be altruistic, people will usually pick the ones that coincide more with their self interest. And in turn, self interest can warp a lot of the outcomes, even if people are trying to help.