Altruism // is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of selfishness.
I read a comment the other day about is there really true altruism. For every action there is an opposite reaction. One does something because it is the right thing to do. Do you feel good about it? I would say yes.
There is a mental affirmation that you did the right thing. It makes you feel good inside even if you do not acknowledge outwardly. You may do something so often you ignore the fact that you do the right thing.
A clinical evaluation would say it does not exist. It would have to be robotic not to have a feeling of some type of payback. But then, someone built the robot didn't they?
What ever the reason, don't stop being nice. Being nice can but shouldn't be analyzed.
Be human, that is all you can be.