Perception of the Narrator in "Shutter Island"

[David]

The book Shutter Island plays with the reader's perception. We are introduced to a character that the reader believes to be entirely reliable - a marshal. The POV of the story is third person, focusing on the main character, Teddy. We automatically sympathize with Teddy because he is the main character. This deep emotional connection is fractured during the final twist of the story, which I won't spoil for you, and is used to make this twist even more shocking. Some parts of the story don't make very much sense though (what psychiatrist would be willing to use an entire island of 300+ psychopaths to cure one psychopaths delusions, especially after previous attempts had failed?