Just as nurturing our ability to love is a way of awakening bodhichitta, so also is nurturing our ability to feel compassion. Compassion, however, is more emotionally challenging
than loving-kindness because it involves the willingness to feel pain. It definitely requires the training of a warrior.
When we practice generating compassion, we can expect to experience our fear of pain. Compassion practice is daring. It involves learning to relax and allow ourselves to move gently toward what scares us. The trick to doing this is to stay with emotional distress without tightening into aversion, to let fear soften us rather than harden into resistance.
From The Places That Scare You: A Guide to Fearlessness in Difficult Times by Pema Chödrön, pages 49-50