I just realized that yesterday I posted a discussion of the ending of Rashomon that could be seen as including "spoilers". It didn't occur to me that anyone would not know the ending to a classic like Rashomon. I mean, would we give a spoiler warning before mentioning that in Citizen Kane, "Rosebud" turns out to be a sled? Or that in Star Wars Darth Vader is Luke's father? This got me thinking about whether it is ever necessary to worry about spoilers.
Consider Romeo and Juliet. Not only do we all know that the two main characters die simply because it is common cultural knowledge, we also know because in the opening scene the Chorus tells us how the play will end. The important thing is that, even though we know Romeo and Juliet will both die, the play still works. There is still drama and even suspense. Every time you watch a well-produced version of the play you think maybe Juliet will wake up in time to stop Romeo's suicide. Of course, she doesn't. And you know she won't. But the play makes you feel as if she might. It works despite your knowledge of the spoilers.
My proposal is this: if a story only works because of a one-time-only shock technique that can be spoiled by knowing too much, then it's not a good story. If a story is capable of being spoiled, it's probably not worth seeing.
Even The Sixth Sense -- one of the most classic "surprise twist endings" of all time -- continues to work after you know the ending. In fact, I think it works better the second time you see it, after you know the twist. (Another classic example is The Crying Game, which I have only seen once, but I suspect it works just as well even after you know that Dil is a man.)
Consider Vertigo. Hitchcock changed the plot structure from the original novel to place the twist a half hour before the ending rather than in the final scene. The studio execs tried to make him change it back, but Hitchcock resisted, realizing that if we know Madeline and Judy are the same person the suspense is more powerful (even on repeat viewings) than the simple surprise of a one-time shock.
Thinking of spoilers reminds me of the line from Memento where Leonard sees his wife reading a beat up book she's read a hundred times before and says "I always thought the pleasure of a book was in wanting to know what happens next." This is, of course, ironic in the context of the film, since the structure of the film is backwards: we see a scene and then we see what happens just before that and then just before that.
So Memento is structured so as the undermine the desire to know what happens next -- instead we want to know what happened before. Thus Memento demonstrates that the true pleasure in a narrative comes from not simply from finding out what comes next but in discovering the connection between what comes next and what came before. But in a well-made movie, there are many more connections than can be seen in one viewing. Even in a murder mystery, it's not just the complex connections between all the clues -- piecing together a plot from the scattered events.
What do you think? Am I wrong? Find me a counter-example -- a masterpiece which can be spoiled by too much prior knowledge.