Is split personality an overused plot twist?

[This contains massive plot spoilers for The Machinist, Fight Club and Secret Window]

When I watch a film where there’s two main characters and one of them is a bit dubious, at some point, I will make a guess that split personality in involved. Usually I’m wrong but the point is, I’m used to this plot twist: towards the end of the film, we realise (usually at the same time as the main character) that the character that is in some way an antagonist is actually the main character’s second personality.

Here's Johnny... Depp

When I first saw Secret Window, I was genuinely shocked that Johnny Depp’s seemingly meek character (Mort Rainey) was actually the split personality of John Turturro’s violent, menacing character (John Shooter). The plot then quickly descends into a pathetic thriller with Rainey writing “shoot her” (if you’re that unobservant, it’s a 'clever play' on the name Shooter) on all the walls in what I can only assume was a desperate attempt to turn this film into something as meaningful to cinema as The Shining. The point is, if this wasn’t the first film I’d seen where a character has split personality, I think I’d have been able to guess pretty damn quick.

Christian Bale: women love him.

The Machinist is another one of those films, but in this one, I guessed not only the glaringly obvious split personality twist, but also half of the plot. Christian Bale is a very talented actor, and probably most people know this film as ‘the one where he lost all that weight’, but it’s actually one of his best (if disturbing) performances. However, even someone with as much talent as Christian Bale couldn’t help the film’s obvious plot twist. The second personality, ‘Ivan’, played by John Sharian, is so obviously a figment of Trevor Reznik’s imagination from the first time he shows up at the factory that the film’s barely worth watching. I’ve only seen this film once, and that was enough, it just didn’t hold my attention in the way that, say, Fight Club did.

"Wait... so I'm also Brad Pitt?!"

The first time I saw Fight Club, however, I was totally amazed. They really did the plot twist well; I suppose that’s down to Brad Pitt and Edward Norton giving really good performances, as well as David Fincher’s direction. The only thing that might give it away is the way Marla Singer acts when she’s around ‘The Narrator’ – she’s sleeping with him, but he thinks she’s sleeping with Tyler Durden. When The Narrator finally realises that he and Tyler are the same person, it’s a revelation for the audience too, and the film goes to a whole new level, with The Narrator trying to stop Tyler from carrying out what is essentially a terrorist act.

Rather than the other two films, which use split personality as a way to draw sympathy from the audience before revealing the ‘monster’ underneath (Rainey has been committing the murders and Reznik has killed someone in a hit and run accident), Fight Club attached the audience to both personalities, before ultimately revealing one to be a bit of a lunatic, and the other to be the ‘sensible’ one. This means that even though the split personality twist happens with a significant proportion of the film left, the audience is still excited as to what will happen to the two characters. Personally, I think that filmmakers should stop using the split personality twist to explain away a ‘bad guy’ or unrealistic character such as John Shooter or Ivan and allow Fight Club its moment of glory!

UPDATE (26/02/2011):
I went to see Black Swan on Wednesday and guess what?! About ten minutes into the film I realised that the plot twist of the film is that Nina (Natalie Portman) is having some sort of hallucination which is basically split personality. 

To Darren Aronofsky: how the mighty have fallen! Why did you have to do that?! It's not original and it's not clever anymore! If your ridiculously predictable film wins Best Picture at the Academy Awards tomorrow, I will be very upset.

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