Four Immeasurable Minds: Joy

The third mind is that of joy, which is wanting all beings to be free from unhappiness and being sincerely happy, without any trace of jealousy, when they accomplish this. Joy counters sadness. It is the state of great contentment and ease.

All too often, we wish to control others. We become irritated when they fail to behave as we wish. If others then praise them for their behavior, we become even more frustrated. But we should learn to feel happy for them. If the person is genuinely happy in what they have chosen to do and their actions have not harmed anyone, then, yes, we ought to feel joy for them.