Movies can’t get away with this. If the audience cannot understand why someone on screen would do something, they don’t chalk it up to the inscrutability of the character, they blame the moviemakers. A movie character whose actions are baffling is judged to be a poorly-conceived character. We don’t buy that they simply had no good reason, because the character hasn’t been able to convince us of that with an internal monologue.
Because we are locked out of their head, it becomes our job to divine their inner thoughts. In some ways, movies are even more about internality than books are, because every action and behavior in a movie is taken by the audience as a clue to that missing holy grail: the internal lives of the characters. If the moviemakers give us clues that point nowhere, then we simply assume that they failed. It would never occur to a moviegoer that a protagonist, like Meursault, might have no internal logic, and no good reason for doing what they do.
Occasionally, a daring moviemaker will attempt to break this rule and shock us by having a hero do something that totally contradicts everything we’ve seen them do up until that point. One obvious example is when Mookie throws the garbage can through the pizza place window in Lee’s Do the Right Thing. After all, Mookie had been the one person in the neighborhood who had consistently defended the establishment.
But this is the exception that proves the rule, because as soon as Mookie does this, the audience become focused like a laser on one thing: going back through everything we’ve seen to find an explanation for what Mookie did. And Lee doesn’t leave us dangling in the wind: he hangs a big sign on one piece of dialogue. We cannot help but conclude that Mookie had Da Mayor’s cryptic words in his head when he did it: “Always do the right thing.” If Lee hadn’t pointed us in that direction by making that the title of the movie, the audience might have said “I dunno, I just didn’t buy it when Mookie did that.” That would have been the movie’s death sentence.