Here's why:
* Intense psychological suspense: The novel focuses heavily on the protagonist's mental state, his paranoia, and the unraveling of his reality.
* Unreliable narrator: The protagonist's perception of events is unreliable, leaving the reader questioning what is real and what is delusion.
* Dark and unsettling themes: The novel explores themes of memory, identity, and the fragility of reality, creating a disturbing and unsettling atmosphere.
* Twist ending: The novel culminates in a shocking and unexpected revelation, leaving the reader with a sense of unease and uncertainty.
Although it has elements of horror, "Shattered" primarily belongs to the psychological thriller genre.