David Gifaldi gets credit for the literary exposition of this concept (and no, you won't find it on his web site–yet) but here's my take. Stories arrive in undifferentiated masses in my mind, sort of the way that dust bunnies arrive under bookcases when I haven't been paying attention. When the stories show up, dust bunny-like, I make a truce with them. You leave me alone, I say, and I won't launch an anti-dust bunny campaign. Some die out at that stage. Others grow, however, and pretty soon a few reach dangerous proportions. This despite my policy of careful negligence.
With me so far?
At this point I need to start paying attention to the ones that are starting to intrude into the fragile balance of my writing world. I can't attend to every single one that shows up. Most of them are just dumb dust bunnies and they'll go away to hide under lesser minds if I just ignore them. I only write out the stories that bother me enough to force my hand.