The trouble is, of course, that they put up that sign saying what flavors they have, with little cardboard inserts to put in or take out flavors, way back when they first opened the store. But they never change the sign or not often enough. They always have flavors that aren't on the list, and often they don't have flavors that are on the list. Children know thiswhether innately or from earlier experience it would be hard to say. What is the main idea of this passage from "How to Eat an Ice-Cream Cone"?