In The Highland Book of Platitudes, Marlais, there's an entry that reads, "Not all ghosts earn our memory in equal measure." I think about this sometimes. I think especially about the word "earn," because it implies an ongoing willful effort on the part of the dead, so that if you believe the platitude, you have to believe in the afterlife, don't you? Following that line of thought, there seem to be certain people—call them ghosts—with the ability to insinuate themselves into your life with more belligerence and exactitude than others—it's their employment and expertise.
