His last service to those who will let him do nothing better for them

"The Landlord does not make the blackness. The blackness is there already wherever the taste of mountain-apple has created the vermiculate will. What do you mean by a hole? Something that ends. A black hole is blackness enclosed, limited. And in that sense the Landlord has made the black hole. He has put into the world a Worst Thing. But evil of itself would never reach a worst: for evil is fissiparous and could never in a thousand eternities find any way to arrest its own reproduction. If it could, it would be longer evil: for Form and Limit belong to the good. The walls of the black hole are the tourniquet on the wound through which the lost soul else would bleed to a death she never reached. It is the Landlord's last service to those who will let him do nothing better for them."

--C.S. Lewis, The Pilgrim’s Regress, pg. 189.