It is our aim to have genuine loving-kindness toward all sentient beings because we see them suffering. In the Mahayana tradition, it says that through our innumerable lifetimes, at some time or other, every single sentient being has been in the relation to us of our mother, our friends, or someone who has helped us. We look at all sentient beings in this way. We feel a deep yearning to help them because they have helped us. When we contemplate in this way, we find that some kind of compassion begins to take place.
Sakyong Mipham Rinpoche in The Tibetan Buddhism Reader, page 101