The best plot twist is one that completely respects the rules. Consider Fight Club and The Sixth Sense, two 1999 films famous for their third-act mindblowers. If you haven’t seen them, please read no further.
Fight Club is about the unstable friendship between two men, one timid and alienated, the other nonchalant and fearless. Near the end, we learn that the cooler man was just a figment of the other’s mind, the bold personality he didn’t dare set loose.
The Sixth Sense is about a boy who sees ghosts, and the child psychiatrist who helps him master that spooky gift. At the end, we learn that the psychiatrist was killed months ago and is himself a ghost. In every scene he was in, only the boy could ever see him.
Both plot twists involve a major character being something we didn’t suspect. Both are fine twists, amply foreshadowed and fitting with their native themes and stories. Yet, I much prefer The Sixth Sense. Why?
Because the twist in Fight Club breaks the rules. I don’t mean the rules of logic – the plot makes perfect sense, and several prior scenes take on a clearer meaning once you know the secret – but the rules of the initial premise. Split personalities aren’t part of it. While the story is psychological, and the main character’s mind is clearly addled, we aren’t made aware that a hallucinated friendship is something that can occur. The surprise has to introduce that rule, that substantial story element. It’s a loud, hefty plot twist.
The Sixth Sense, meanwhile, is overtly about ghosts. We learn about them early on. Therefore, the surprise doesn’t have to introduce any new rules, only make one decisive connection: This character is also a ghost. It’s a sharp, delicate plot twist.
You could say it’s a question of efficiency. All The Sixth Sense has to do to shock you is move a piece on its chessboard. Fight Club has to throw out the board and reveal the true board underneath, the rules that were secretly in effect all along.
Both types of twist take skill to do right. But I’m always more impressed with the elegant Sixth Sense type. I like it when a story can shock me without breaking a sweat.