Most English teachers have somewhere in their pocket that lesson about Edgar Allan Poe's "The Telltale Heart." The story is narrated by a guy who's clearly in the grip of madness, and so we have to filter what he tells us through our understanding that what he's reporting is not what another observer might see. He's an unreliable narrator, a literary trick that Poe perfected, which is why for all Poe's reputation as a teller of scary tales, there's nothing in Poe that is undeniably supernatural. Mostly it's just subjective madness, filtered through the unreliable narrator's twisted lens.
Narrators can be unreliable for a variety of reasons; they may be deliberately misleading or simply unaware of their own blind spots and biases.
Poe is obviously not the only author to present us with unreliable narrators. And even authors who are not always associated with the technique present us with versions of it. Ernest Hemmingway is often cited as an example of an author who presents unvarnished, cold, hard views of the events in his novel, but even his narrators require us to sort out what is really happening. Take this snip from The Sun Also Rises:One of them saw Georgette and said: "I do declare. There is an actual harlot. I'm going to dance with her, Lett. You watch me."