From The Faraway Nearby by Rebecca Solnit
Pain serves a purpose. Without it you are in danger… The disease (leprosy) strangles nerves, kills off feeling, and what you cannot feel you cannot take care of: not the disease but the patient does the damage. You begin nicking, burning, bruising, abrading, and otherwise wearing out your fingers, toes, feet, hands, and then losing them… The nerveless part of the body remains alive, but pain and sensation define the self; what you cannot feel is not you; what you cannot feel you do not reality take care of; your extremities become lost to you. Pain protects. You flinch, you blink, tears flow. With leprosy, you might stop blinking, so your eyes go dry, or you rub them too hard and scar the cornea, or fail to notice some injury at all. Thus blindness is a common consequence of the disease… If the boundaries of the self are defined by what we feel, then those who cannot feel even for themselves shrink within their own boundaries, while those who feel for others are enlarged, and those who feel compassion for all beings must be boundless. They are not separate, not alone, not lonely, not vulnerable in the same way as those of us stranded in the islands of ourselves, but they are vulnerable in other ways. Still, that sense of the dangers of feeling for others is so compelling that many withdraw, and develop elaborate stories to justify withdrawal, and they forget that they have shrunk.