An upside-down shelf is an unusually accurate example of an Egg of Columbus:

An egg of Columbus or Columbus' egg refers to a brilliant idea or discovery that seems simple or easy after the fact. The expression refers to an apocryphal story in which Christopher Columbus, having been told that discovering the Americas was inevitable and no great accomplishment, challenges his critics to make an egg stand on its tip. After his challengers give up, Columbus does it himself by tapping the egg on the table to flatten its tip.