We all know that a plot is a chain of cause and effect: one thing leads to another, which in turn leads to something else, on and on in ways that should seem clear -- at the very least, in hindsight.
We also know that a plot hole is a break in this chain: something happens without sufficient cause, character motivation, or explanation:
KUZCO: No! It can't be! How did you get back here before us?
YZMA: Uh... how *did* we, Kronk?
KRONK: Well, ya got me. By all accounts, it doesn't make sense.
YZMA: Oh, well. Back to business.
Along with plot holes, we can also have what I call thought holes. These are gaps in the reasoning behind a story, in its concept, in its background details, or in both.
One example crops up in "The Dreaming City" by Michael Moorcock, a story based on certain assumptions:
-- Elric is the rightful heir to the throne of the dreaming city.
-- While he is out wandering in distant lands, he is declared a traitor and outlaw by his cousin, who now rules in Elric's place.
-- Elric wants vengeance against his cousin. To this end, he is willing to have the dreaming city invaded and sacked by sea raiders.
-- The point of attack will be the main harbour, which is concealed behind a maze. Elric knows how to pass through the maze, and so he must lead the attack. He must also conceal the approach of this fleet with a magical fog.
All in all, a risky plan; so much could go wrong. But consider this: a day or two before the raid, Elric, in a single boat, sails to the dreaming city to set up one of his own personal schemes:
"Elric knew that he dare not risk entering the harbour by the maze, though he understood the route perfectly. He decided, instead, to land the boat further up the coast in a small inlet of which he had knowledge. With sure, capable hands, he guided the little craft towards the hidden inlet which was obscured by a growth of shrubs...."
All of this happens in full daylight:
"On foot, Elric strode inland.... At last he came to the city."
"Elric, his hand ever near his sword-hilt, slipped through an unguarded gate in the city wall and began to walk cautiously through the ill-lit streets...."
I have no head for military planning, but I still have to wonder: if I were to lead a potentially-disastrous, frontal attack on a city, and knew of an unguarded back route where a secondary line of men could reach the city in full daylight without being observed, would I not want to use this tactic, at the very least, as a diversion?
When Elric snuck into this hidden cove, he could have brought several men along with him, shown them the route, shown them the unguarded gateway, and then returned them to the raiders' fleet where they could develop plans for a back-up force. I would have done it. Hell, why not?
Moorcock never explains why such a plan could never work, because he never mentions the possibility. He sets it up in the reader's mind, but then ignores it.
A thought hole!