I believe we act based on self beneficial deed.
Aware or subconsciously we act based on our belief system of morality, spirituality or simply egoism. It’s natural.
You sell they pay or the other way around.
If you give something or a favour to others you naturally expect some sort of compensation. Maybe not right away but in the future. He or she will return the favour when you need it.
When you need a help. You are indebted when help is given. And it has to be paid.
Nothing is really free. If you are believer, your God also say with terms and conditions on the holy book ” What’s in it for me?” .
Perhaps accepting that “gain and lose” in our belief system will speed up the self mastery during our existence.