There are two great proximate causes for compassion: suffering and wisdom. Suffering opens the heart and wisdom lets us see the fragile impermanent nature of all things.
Q&A at end of talk
The near enemy of compassion is pity; the far energy is cruelty. But more often the obstacles to true compassion are wanting to fix rather than be with suffering.
The ability to put oneself in someone else's shoes is the doorway to compassion. Once there is compassion then forgiveness, connection and genuine metta naturally follow. This talk includes a teaching from Thai master, Ajahn Maha Boowa, on the power of empathy.