The other day I was writing about point of view and the value of separating a character perceiving, noticing, and understanding - and I realized that there was a connection there with the idea of unreliable narrators. I've posted about unreliable narrators before, here, and one of the things I remarked was that every narrator can be unreliable to some degree.
Because anyone can make a mistake.
Let's say you have an event - say a line uttered by someone - that your character witnesses. And let's say that your character mishears that line, because he or she is in a state of shock at the time, having just....something. Learned terrible news, or had an arrow shot through her arm, or discovered his lover was unfaithful, etc.
First of all, let me refer to the tried and true (if frustratingly opaque) adage, "show don't tell." In a close point of view, I personally would rather not be told by the narrator that a character is in shock and can't hear properly - that dumps me right out of the narrative. So what I would look for is evidence inside the text that the character is in shock. This would be things like incoherent thoughts, distraction by pain, etc. that you can demonstrate easily if your narrative is directly reporting the internalization of your narrator. Here's an example (made up on the spot :) ).
"Donner fell back, staring at the arrow that had impaled his arm. Anika was shouting - God, he couldn't move his fingers, he'd never be able to join the guard now! A figure in black loomed over him, while her footsteps thumped up behind - was this the physician?"
Ok, so at this point if you have Anika say something, the reader will know that Donner is in a highly distracted state and not able to string thoughts together rationally. The choice for the writer then becomes whether to have Anika actually deliver the line.
If it's not important for the reader to know the content of Anika's message, then you can just have Donner pass out, or you can figure some message was delivered when she shouted but Donner didn't get it. If this is the case, you can have Anika refer to this event later, saying something like "but I warned you that that was Ghori coming to finish you off - I couldn't have shouted it any louder." To which Donner could reply "Good thing you'd brought your broadsword, Darling."
On the other hand, if it is important to the reader to know the message content, you can have her deliver the line perfectly clearly. "Watch out, Donner, that's Ghori - and he's got the crystal!" Donner can perceive the words, allowing the reader to do so also, but so long as he doesn't react to them in a way that shows he has noticed or understood, he can show his lack of comprehension later and readers will not be surprised or confused.
Close rendering of subjective experience is a great way to show a character's understanding without leaving readers behind. In the case of a large battle, for example, the author would do well to know what is going on behind the backs of the nearest soldiers, but the point of view character will only perceive the most local evidence of that larger picture. As a writer, you can choose to use other points of view to put the larger picture together later.
If you happen to be working with a very unreliable narrator - an insane person, for example, or someone who is drunk or high, then all of these tools for the separation of perception and judgment - even action and judgment - will come in very handy. Cold Words (which is written in first person) contains a sequence where Rulii eats a drug-containing plant and then runs home: I had to take him from rational to irrational, gradually removing all of the kinds of thoughts that showed measured judgment, before I could finally have him take actions that were impulsive and dangerous to his friend Parker (and very uncharacteristic of Rulii's normal personality). In that scene, I reported Parker's actions only in the most basic way, and I wrote all of Parker's lines quite clearly, but never had Rulii respond as though he took them seriously.
A final observation: one of my pet peeves in reading stories is when I feel an author is keeping secrets from me. My measure of that comes from the choice of point of view. In a movie, where I have no evidence of people's mental states, I'm more willing to accept that "wait, that guy was working for the secret society all along." If I've been in his head, though, his motives are very important to his internalizations and his choice of action, and if the character knows something, I feel I should know it too. I actually find it more suspenseful when I know who's working for the bad guys, and I know that the good guys aren't aware of the same things that I am. This is one of the reasons why I tend not to use omniscient point of view, because then my authorly hand is more obvious, and I think readers can tell when I'm deliberately hiding/avoiding certain information. But when I can filter the story through a character's subjective experience, then I have a perfectly good reason for a piece of information to be secret: it isn't known to the POV character.
I love point of view tools. They can do some really amazing things.