That technique where you slowly realize the person telling you the story isn't just lying to you, they're lying to themselves... I gravitate toward thrillers that use it as a structural cheat code. 'Gone Girl' is the obvious one, but the execution is still a masterclass. Flynn builds such a meticulous, sensible-seeming reality through Nick's chapters, only to have it shattered by Amy's 'Cool Girl' manifesto. The hidden motive isn't just a plot twist; it's a character's entire philosophy of performance and revenge made weapon. Then there's 'The Silent Patient' by Alex Michaelides. The narrator is a psychotherapist, which already sets up this expectation of insight and truth-seeking. Watching him project his own obsessions onto his mute patient while meticulously obscuring his own past is a slower, colder kind of unraveling. You're not just figuring out 'whodunit,' you're figuring out who this narrator really is, and the motives are always more personal and more pathetic than any grand conspiracy. It makes the final pages feel less like a victory and more like you need a shower.
What's more interesting, though, are the subtler uses outside of crime. Kazuo Ishiguro's narrators, like Stevens in 'The Remains of the Day,' are unreliable through a filter of repression and duty. Stevens is so committed to his ideal of 'greatness' and 'dignity' in service that he cannot—or will not—interpret his own feelings for Miss Kenton, or his employer's Nazi sympathies, with any honesty. The hidden motive is self-preservation of the identity he's built. You have to read the gaps, the things he almost says, the moments he changes the subject. The revelation isn't a shock, it's a heartbreaking accumulation of everything left unsaid.