Originally Posted by Roger Ebert
Law of Economy of Characters
Movie budgets make it impossible for any film to contain unnecessary characters. Therefore, all characters in a movie are necessary to the story—even those who do not seem to be. Sophisticated viewers can use this Law to deduce the identity of a person being kept secret by the movie's plot: This "mystery" person is always the only character in the movie who seems otherwise extraneous.
I've used this law on more than one occasion, especially when watching any of the C.S.I. incarnations. The thing that really
brought it to mind was after reading The Bone Collector
(based on a recommendation in a request for puzzle fiction
): At the very beginning, they mention the serial killer case that incapcitated Rhymes turned out to be committed by a cop, and I was thinking, "They're not foreshadowing that overused cliche, are they? That one of the minor cop characters, who'd be familar with Rhyme's methods, would be the one who did it?" However,
Which was a great disappointment to me, because it was almost like the author said to himself, "Well, who's the most unlikely current character I can make the killer regardless of logic?" The answer, to me, was completely unbelievable.
So my question is, whether in film, TV, or literature, can this law be circumvented? Or will the mysterious perpetrator always be someone we've already met in the story? And... which is better?