To the pain means that the first thing you lose will be your feet below the ankles. Then your hands at the wrists, next your nose. The next thing you lose will be your left eye, followed by your right. Your ears you keep, and I'll tell you why: so that every shriek of every child at seeing your hideousness will be yours to cherish; every babe that weeps at your approach; every woman who cries out, “Dear God! What is that thing?!” will echo in your perfect ears. That is what “to the pain” means; it means I leave you in anguish, wallowing in freakish misery, forever.

It’s from The Princess Bride, as is the explanation below.