Compassion is the desire to help someone who is suffering.
Sympathy is feeling sad for that person.
Empathy is feeling the same sadness that person feels because you've imagined yourself in his or her shoes (or perhaps been in a similar situation before) and understand what it is he or she is feeling.
A headless moth could feel compassion for his blind sister. Though he can no longer feel for lack of a head, he bumps his blind sister from her trajectory toward the stack of pancakes and thereby sealing his fate as moth pancake topper.
Cursed be the breakfast maker operating in the pre-dawn darkness.
Though he is crafty, no dim light saved his children from consuming compassionate headless moths stuck in Aunt Jemima's breakfast syrup.
a headless moth cannot feel compassion and cannot fly without a head