Parents do a lot for their kids and hence expect a few things in return (maybe respect, maybe one visit per year, maybe don’t do drugs, …)
Friends do a lot for friends. Helping friends in need, spending a lot of time/money/energy for them, calling them even when they don’t pick up, ….
A spouse does a lot of things for their partner. Sacrificing/deprioritizing their career, moving across the country/world, doing a majority of housework, .…
No more examples. You got the drift.
It seems that we do a LOT for others. But we don’t.
If you dig deep you do everything for yourself. For example, suppose I have a daughter named Angel. I do a lot for Angel and make a lot of sacrifices for her. Imagine a scenario where instead of Angel, I had a different daughter. Not just a different name, but a different human being altogether. Suppose this new daughter's name was Bella. I would have done all the things and sacrifices for Bella as well. So objectively I am not doing anything for my daughter Angel. I am doing everything for MY daughter. Who my daughter is matters less but she is my daughter matters more. I am doing everything for my daughter and not for Angel. Hence am doing everything for myself.
The same thing can be applied to my friends, parents, or strangers.
You don’t help or behave well with strangers as a favor to them. You feel good about yourself after helping strangers hence you do whatever you do for yourself.
When you do things for others, you expect in return from them. But when you do everything for yourself, you do it because you want/need to do it.
You are not doing any favor to anyone. You are doing everything for yourself. I am doing everything for myself.