David Fincher's Fight Club turns 20 years old (!) later this year, and ever since it first hit cinemas, audiences have been fascinated by its intoxicating blend of acid-tongued nihilism and blackly comic social satire.
And of course, Fincher's film is often cited as boasting one of the best-executed plot twists in cinema history, with the climactic revelation that - spoilers! - that anarchic soap salesman Tyler Durden (Brad Pitt) does not exist, but is in fact a dissociated personality in the mind of the unnamed narrator, commonly referred to by fans as Jack (Edward Norton).
Though that's enough of a mind-bender for one movie, there's a fan theory that's been gaining significant traction in recent years, that another plot twist is hiding in plain sight, that Tyler Durden isn't the only fabricated character in the film.
As it turns out, femme fatale Marla Singer (Helena Bonham Carter) is also a personality created in Jack's mind.
Fight Club as a whole is defined by its unreliable narrator, and in many ways that's what makes it so fun to dissect. There is no strictly-defined objectivity to the events we see play out on screen, and Durden himself even says as much when explaining the various perspectives through which Jack views Durden's acts.
The viewer is largely left to decide for themselves exactly how events play out, namely what is reality and what is imagined. This is obviously focused primarily on Tyler, but when examined through the lens of this theory, it can also apply to Marla too.
The primary theme of Fincher's film is of dissociation, both in terms of its protagonist's mental state and also how he relates (or doesn't, in fact) to society.
This is ultimately what sets the stage for an internal struggle between two diametrically opposed - and yes, fictional - forces, Tyler Durden and Marla Singer, who represent conflicting possible futures for Jack.
And with that in mind, let's take a deep dive into the most convincing clues that Marla doesn't actually exist...
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