[— Karen Myers —]
The above image of the underground city of Cappadocia sparked a metaphoric response.
Everything you write about has hidden depths, just like real things. Places have histories, societies have generated customs, predators and prey have evolved together, planets have continental drift and subduction.
And people… people are swarming with interior experiences, tendencies, impulses, and emotions. Everything a person does depends not just on the superficial trigger, but on what he contains within and how he has reacted in the past.
Most of this subterranean content is hidden — the hidden reasons for personal choices, the hidden backgrounds for present situations, the hidden places of refuge.
Maybe the person doesn’t think about it. Maybe if you challenged him he would pretend there’s nothing beneath the surface to challenge his will. But there’s all sorts of life and potential complexity underground in all of us. As writers, we have to understand what stirs our characters — why they act the way they do — even if they don’t understand it themselves. More subtly, we have to understand how events in our stories add to the underground components of our characters’ behaviors.
Can a character become conscious of his drives? Can he change them? Bring them to the surface? Does he bury the traumatic ones and pretend that they no longer exist?
Or will he be surprised when something rises from the depths and overpowers his conscious intent?
The underground city of Cappadocia is estimated to have held 20,000 people in emergencies. Just think of all that lying beneath the surface of, well, everything.
We’ve all read stories where the obscure history of places or things rises to importance — the sword of doom, the lost treasure, the deadly pit forgotten beneath the city until the earthquake.
But what about people and their hidden depths? Not the stories of people-as-fated-objects (the vanished prince born to save the country), but stories where the subterranean components of people serve as refuges, or as unexamined components of behavior — what memorable instances of that have you read or written?
Mad Genius Club 
Do they go la la la I can’t hear you and so develop affected ignorance
If I understand your question correctly, I think Dorothy Grant’s _Between Two Graves_ shows the “unexamined components” of AJ’s behavior.
In order to see what you are asking, I think, a person or character has to be known first and the explanation must come later. Many (good and great) stories are about how people are acquiring that hidden stratum that will serve them later in “life” but we don’t always see “later” because the story arc is about the growth.
And on reflection, perhaps Frodo? Completely different from AJ.
Had to do this in the fanfic thing.
Basically in cannon there was a odd relationship between A and C. However, cannon *never* explains why A behaves the way they do towards C. And the interactions between those two characters ended up being a very important part of the story.
So I not only had to come up with a reason/backstory that fit the universe, I also had to figure out who else would know and why they don’t ever tell anyone (because it’s not cannon and needed to remain cannon compliant if the author ever did explain things) and how they talked about it without actually telling anyone what was going on.
That was a real brain bender, but it was a good experience, and I think it worked out in the end.
Maybe Han Solo? He came back and shot Vader out of the sky. By his self-presentation he shouldn’t have. Defining character moment.
On a tangent: question for the horde: have you ever had a story that needed to be read out of order?
I’m wondering if one of the current sticks with the current WIP is the male lead’s origin story is slogging because he starts in an emotionally dead place, and telling the story out of order would give more of a “this is why I should care” and “how did he get from A to B?” to it?
If it feels like a slog in his POV, maybe try it from someone else’s or start later in the story. People din on about “character growth” but it doesn’t mean you have to start with them at their absolute worst or least appealing.
The slowly unfolding story of why Arthur Saldovado is so cold, then so protective of Lelia and Deborah (and the boys, but they are boys, and Hunters, so that’s different). It’s not just the Hunter clan culture, but his personal past.
In the WIP, Master Osgar, the herbalist that Saxo eventually trains under. He absolutely will NOT tolerate gossip. He’s also unmarried, but has very nice furnishings for a bachelor herbalist. The two are related, but Saxo doesn’t learn why until the last chapter of the book.
I’m sure I’ve read others, but my brain is not running on all 6 cylinders tonight.