There is a standard remark that just about anyone starting their philosophical journey realizes. And that is that everything anyone does is only for themselves. I've gotten a little but strong opposition to this. But they were always based on emotion, not logic. As such, the statement can be qualified that emotionally they may be doing it not for themselves. Although, ultimately, it is for themselves.
A person only does that which they decide to do. There are three cases where a person does not, but they are easily explained.
1) If someone else moves their body without them doing so.
2) A reflex or unconcious action.
3) A situation where all choices are bad.
The first case the *other* person is doing the action. In the second case, the body is taking the action, not the concious person. In the third case, the person still chooses the better of the two, although regretting the situation, the choice itself is still made without regret.
A person can do a thing for a person. That person can be either oneself, of another. If oneself, it is obviously being done for onesself. When it is for another, it is not as easily seen. So, the reason for doing for others must be explored.
When doing for others, the question is, "why?" It is because the person decided to do it for the other. If based on choice, the person had ultimate control. And this person chose to do it for the other person. Regardless of why the person chose to do it, the person chose it, and then did it. And that means it is done for oneself.
One may retort and say that the choice itself can be for another, and thus the choice itself is not for oneself. The rejoinder would be that the choice is based on liking the other person, or doing for another. If a person decided to do a random act of kindness to a random person, it is being done to satisfy the person's desire to do that. Without the desire, it would not have been done. If asked to do it by another the person will only do it if the person makes a desire to do it first.
Hmm.. I guess it can be said that people only do things to satisfy their own desires. That doesn't sound correct. That needs further thought.