An argument can be made that all actions people take are for their own self-interest. Even things like helping the community is done for reciprocal benefits for yourself plus the general increase in respect.
Another point is that if all people just act for their own self-interest, they will have a better life themselves, and if everyone does the same, some sort of proper balance will be achieved.
I have been having some occasional discussions with my friends over this. I personally disagree, but would love to hear what others have to say. Feel free to discuss!
No, most people wouldn’t recognize their own self-interest if it stopped them on the street. Neither are people all that great at identifying morally correct actions on the fly.
This is why formulating ethics into easy-to-remember precepts is a time-honored tradition. Most people are too lazy or inexperienced to do their own ethics work.