Selfish

Was just wondering what is limit to which one can think of his benefit without being selfish.
Or if there is anything known has thinking of yourself without being selfish.
These days am just skeptical about anyoen and anyone being nice to me 'coz from past 5 months I have seen only one thing that if someone is being nice to you there has to be hidden agenda behind it.
and kills you to just think that its not you for which people approach you but what can they get from you for which do that.
Anyways lousy thoughts,guess will do some cheering up exercise to come out of this kinda mode or thought process