a) Sometimes we help others merely to get something in return.
b) Sometimes we do it to create a win-win for us and them.
c) And sometimes it’s purely for the benefit of the other person.
Though (c) is often a win-win, because the giver experiences the joy of giving and spares him or herself the pain of seeing someone suffer.
We’re capable of feeling that way about animals too. We are living, conscious beings, aware of our connectedness and likeness to other living beings. Plants are alive too, but as far as we know they don’t experience suffering. It’s suffering that we’re concerned with. We want to limit not only our own suffering, but also the suffering of other beings.