One literary device that teachers refer to, and which students sometimes write essays to analyze, involves the concept of the unreliable narrator, someone reporting the details of the story who is in some way not trustworthy as the sole "explainer" or interpreter of events. The person's version of the situation becomes clear, quickly or gradually, as full of holes.
One short story many have read, in which the narrator clearly cannot be believed, is "The Tell Tale Heart" by Edgar Allen Poe. The main character's frequent protestations of his sanity and cleverness show up shockingly against the information he then provides about what he does and why he is doing it. Such discrepancies several times in the story lead the reader to determine that indeed the narrator suffers from a severe delusional disorder and mania.
At times, a reader scratches his or her head when a short story comes to a surprising ending, and it is only then that the narrator's unreliability becomes apparent, if the story is to have any clear meaning or aspects are to be reconciled. It can be argued that the narrator of "Charles," a woman whose son comes home with tales of a beastly new boy in his kindergarten class, does not fully explain matters because she remains oblivious to the reality of the situation until the end, at which point the ironic ending makes this clear.
When an author employs a child to act as reporter, this narrator is almost certain to understand less of what occurs around him or her than the reader will. The Adventures of Tom Sawyer provides an example of this situation.
A narrator who has severe mental limitations, such as Charley Gordon in Flowers for Algernon, brings to life aspects of what occurs around him by expressing puzzlement and confusion about them. This novel works particularly well partly because he becomes a reliable narrator for a time, when he gains more intellectual strengths; later, as his condition deteriorates to even less than what he was capable of before, we see again, this time even more markedly, that he doesn't interpret or understand what goes on around him as fully as we the readers can.
Many consider Nick Carraway, the narrator in The Great Gatsby, to be unreliable because he is infatuated with the image that Jay Gatsby projects, to the point that he does not process the novel's events with any moral response. Only as the reader begins to note his lack of outrage, shock, concern for others, or disgust does it become clear that his representation of events surrounding this iconic man is tainted by his adulation for Gatsby.
The uses of the unreliable narrator often connect in some way to theme; discover an underlying statement about human nature that the author seems to be making, and the use of an unreliable narrator will make sense in that context. F. Scott Fitzgerald wrote about people in the Roaring Twenties who were morally bankrupt, and Nick is no exception, no matter how he holds himself as separate from the others. The fact that he seems to see himself as outside the the group actually verifies that he interprets the situations without objectivity that they all face and therefore cannot be depended on to explain matters fairly.