Stahl's Keys (a.k.a. Tolkien's Keys)

I was watching The Hobbit: The Desolation of Smaug yesterday and devised a variant on Chekhov's Gun.  Stahl's Keys (a.k.a. Tolkien's Keys) is the rule that "If a ring of keys is set on a hook, it ought stay there."  Basically, if the narrator observes a character doing something very mundane but still mentions it, there must be some sort of resulting plot point.  You shouldn't note actions that don't matter to the story for one; for two, if you include foreshadowing like this in a story and don't deliver on that foreshadowing, readers are likely to take everything they think is foreshadowing with a grain of salt.  This isn't good, especially for writers who rely on foreshadowed information coming together during the climax and/or resolution of their stories.