Śāntideva, states:
Whatever suffering is in the world
comes from seeking your own happiness,
while whatever happiness is in the world
comes from the wish for the happiness of others.
What need is there to say more?
The childish pursue their own interests,
while the buddhas act for the welfare of others:
observe the difference between the two.
~ A Guide to the Bodhisattva’s Way of Life 8:129–30, 28b3.