There is a sutra story that goes like this:

Once upon a time in the kingdom of Kosala there was a king who asked his daughter the princess, ‘Dear child, as for you, is there anyone whom you love more than yourself?’
The princess gave the matter some thought and said, ‘As for me, there is no one whom I love more than myself. How is it with you?’
Pressed for an answer the king was forced to admit that he too loved no one more than himself.
However, their answers did not sit right with them, and so they left the palace to seek the Buddha’s advice.
The Buddha told them, ‘O King, so you love yourself the best. All people love themselves the best. What we must never do, though, is to love ourselves to the point where we inflict harm on others.’*

When we think only of our own happiness, how quickly we forget that the other persons in our life are also seeking happiness for themselves. Not only that. At times we are so intent on getting happiness for ourselves, even if it means getting rid of whatever stands in our way. It is at this point that conflicts and wars erupt. We cannot seek happiness only favorable to ourselves. We must seek a situation where everyone is happy.
When the happiness of others is our happiness, and their sadness is our sadness, this is called the heart of compassion. This is the heart of a Buddha.
When a person becomes more responsive to the feelings of others, is this not a sign of their development as human beings?
If we remove the hedges thrown up around us and cooperate in one another’s efforts to live, we truly come to life as human beings.