When you do something nice for someone, the "reward" is that it deepens your relationship. When both sides are invested in the relationship, they both enjoy the fruits of this. Doing a favor so someone will "owe you" is often a sucker's game, and it only works within a mutually accepted framework.

Oh, when I say "there was a story", I mean actual news articles. This isn't an apocryphal anecdote. But I'm not looking to rebuild the part of my brain that indexed this stuff for easy retrieval.