The Triangle in my opinion lies on that border that almost has the viewer thinking that it’s not horror. It is horror in my opinion and it fulfills that in the literary aspects of it. In literary form, it’s closest to Greek tragedy which it already references by thematically bringing up the element of Greek Myth into the weave of the story; the story of Sisiphus foreshadowing and evoking the eternal trap. Examining the element that brings the emotion of horror to both the character and us as the audience, I think that horrible twist lies in the fact that as you start the experience from the perspective of this main character you follow and the sequence of events she chooses to play out eventually begin to alienate you from her till the point that she reaches full circle into the clock cycle of events.
Following the earlier parts of H. P. Lovecraft’s Supernatural Horror in Literature where he makes the point of saying how there is horror in the unknown that strikes us with fear and awe and further leaves us dumbfounded by a lack of reasoning/causality level with our own and the known, the movie, I think, accomplishes this in how at the point where the movie ends where it begins after seemingly showing us that she may have escaped the cycle only to pull the wool over us and further cement her isolation in her little maze. The Jess we see at the start who wears a dress never makes it to the docks. The cycle has always been about the Jess who arrives at the platform, boards the ships, iterates on the ship thrice, escapes, kills the Jess outside the loop, gets her son killed, and again arrives at the docks with the help of the taxi driver.
What I find novel about this horror story is how, in a manner of speaking, the monster is everything that isn’t the main character. The monstrous or numinous being that is cosmically bigger than the main character and us is the whole construct of a private hell of sorts for this character which is what ties us back to the theme of Greek Tragedy and in a sense the ideas of Fate, Destiny, and not being able to escape from either. The Greeks lived by this and passed on the stories of inescapable consequences of our actions, slights, and the fancies of beings and powers far above us. This exact fatalism guided this more primitive line of thinking and fenced people into an order made clear by the benign gods and the punishment of the malign. The idea later becomes that her suffering is a product of her mistreatment of her own son, pushing the idea that her fate is this entrapment.
Through Freud’s examinings of the Uncanny, part of our experiencing the uncanny stems from the character of Jess being made to confront the iterations of herself within the maze. Freud explained that this re-experiencing aspects of our lives long forgotten, or rather that remind us of our “earlier psychic stages”, can be seeing the ghosts of our past. Jess finds herself having to contend with the idea of those masked iterations of herself as killers, further reminding her of her incomprehensibly feral and monstrous side of her past personality. She faces the monster head on when having returned to her own home after escaping the ship she witnesses herself mistreating her autistic son. That moment when the movie concludes and you realize she exists in this bubble of, like I said, her own private hell. The imagery I can ascribe to this is like finding that the monsters exist inside and outside your cage. The unnerving horror also exists in the fact that after realizing all this, we as viewers see her existing but neither living nor dying; a sad non-end.