The author makes a tacit deal with the reader. You hand them a backpack. You ask them to place certain things in it—to remember, to keep in mind — as they make their way up the hill. If you hand them a yellow Volkswagen and they have to haul this to the top of the mountain—to the end of the story—and they find that this Volkswagen has nothing whatsoever to do with your story, you’re going to have a very irritated reader on your hands.