In the case of attachment to someone, you wish that person well but it is based on an identification with him or her as “my friend, my son, my daughter.” This identification and this feeling of ownership or territoriality is related to wanting some kind of return. You enjoy the happiness of that person because you have identified with him or her, and therefore in essence it is just wishing for your own benefit. Such attachment can very easily turn to aversion, anger, and hatred. That is the difference between compassion and attachment.

-- Khenpo Kathar Rinpoche