They Just Don't Get It

A character, or more often a whole group of people, has something elementary and basic explained to them, but for some reason, they just aren't getting it. They aren't being deliberately obtuse and stupid. They simply do not understand the rather obvious implications of what has been said to them. To the character trying to do the explaining, and to the audience, the train of thought is painfully easy to make work logically, but the target simply isn't getting it.

Sometimes this is because of Selective Obliviousness or Obfuscating Stupidity, but only rarely does the audience know this at the time.

Anime & Manga

 * In the Yu-Gi-Oh!: The Abridged Series movie, when Yami finally confronts Anubis, he asks him why we wants to destroy the world. Anubis doesn't understand the question, even as Yami exasperatingly repeats that he surely must have a reason for destroying the world, considering all the trouble he went to to do it.

Film
"Vanessa: And then there's this. (shows Austin a dental hygiene kit complete with floss, toothpaste and toothbrush) Austin: Let me guess. The floss is garrote wire, the toothpaste is plastic explosives, and the toothbrush is the detonation device. Vanessa: No, actually. Since you've been frozen, there have been fabulous advances in the field of dentistry. Austin: What do you mean?"
 * This happens in Mystery Men when one of the characters realizes that Captain Amazing is just Clark Kenting. The other characters don't understand the way this train of thought works, since without glasses, Captain Amazing would not be able to see.
 * Idiocracy. Joe Bauers encounters this problem in every scene where he tries to explain something to someone, or tries to be subtle about something, because everyone in the future is Too Dumb to Live. The most notable instance is when he is explaining to the Cabinet his plan to use water on crops instead of Brawndo.
 * Austin Powers: International Man of Mystery, during a discussion of Austin's teeth.


 * Cleverly inverted in the scene where Scott Evil wonders why they are going to all the trouble of putting Austin and Vanessa into a Death Trap.

"Scott Evil: I have a gun. In my room. You give me five seconds, I'll get it, I'll come back down here. BOOM! I'll blow their brains out! Doctor Evil: Scott, you just don't get it, do ya?"


 * In Talladega Nights: The Ballad of Ricky Bobby, Cal Naughton Jr. just doesn't seem to understand why his friendship with Ricky Bobby should be affected by something trivial like Cal sleeping with Ricky's wife.
 * It's a popular phrase in film.

Live Action TV
"Jeff, in a sneak preview for Redemption Island: "He still doesn't get it! He still thinks that everybody loves him.""
 * One sketch on All That has Superdude, played by Kenan Thompson, being confronted by an impostor played by an 11-year-old Amanda Bynes wearing a copy of his costume. The townspeople, incapable of determining the fraud based on physical appearance, are further unable to distinguish the difference in Power Levels when they see Superdude bending a giant pipe and the impostor tearing up a piece of paper.
 * To be fair, the impostor got a Theme Music Power-Up just as Superdude did.
 * Russell Hantz still has no idea why he lost Survivor twice in a row, despite everyone from interviewers to fellow contestants, to Jeff Probst himself explaining that you just can't piss off the people who will be casting the votes that decide whether or not you get the million. Instead (like some of the Hantz Nation), he's going with the theory that the game is flawed - especially since the two girls he lost to beat him by being less reprehensible than himself. Even Parvati was seen as the lesser of two evils in Heroes vs. Villains (and received three jury votes).
 * He and his allies also didn't realize why he was evicted from Redemption Island so early despite that unlike the first two times he played, people knew who he was, and he had made no visible effort to change his game. (There is more or less no excuse outside of having never seen the show before for not knowing Russell's game by now.)

"Cat [to Rimmer]: What is it? Rimmer: It's a rent in the space-time continuum. Cat [to Lister]: What is it? Lister: The stasis room freezes time, you know, makes time stand still. So whenever you have a leak, it must preserve whatever it's leaked into, and it's leaked into this room. Cat [to Rimmer]: What is it? Rimmer: It's singularity, a point in the universe where the normal laws of space and time don't apply. Cat [to Lister]: What is it? Lister: It's a hole back into the past. Cat: Oh, a magic door! Well, why didn't you say?"
 * Red Dwarf has this exchange from the episode "Stasis Leak":

"Xander: Wait, guys... Spike: Well look at the big brain on you! I've only been saying that for the last two weeks!"
 * Not to mention the Trope Namer for Everybody's Dead, Dave, where Lister simply cannot comprehend that all of his shipmates have been killed.
 * In Buffy the Vampire Slayer's fifth season, the fact that  This, of course, drives Spike to utter distraction.
 * Particularly when the spell no longer works:

Western Animation
"Mallory: Most secret agents don't tell every hooker from here to Hanoi that they're a spy! Archer: ...then why be one?"
 * The centerpoint of the Chicken Boo sketches on Animaniacs is that the Only Sane Man is trying, and for most of the sketch failing, to explain why Chicken Boo is, in fact, a chicken.
 * This happens pretty often in South Park, where one of the kids tries in vain to explain the facts of the situation to the adults, and the adults either just don't get it or else get it horribly, horribly wrong. For example, in two separate episodes, Stan and Kyle (respectively) try to demonstrate that psychics are fake by explaining their methods. Both times, they are revered as psychics themselves.
 * Another episode has a moral equivalent to this when Butters is arrested for toilet papering a house when the main characters were the ones who really did it. Cartman literally cannot understand why the others think this is a bad thing, since he's basically a sociopath who simply does not care about other people in the slightest.
 * In Archer, the titular character is unable to grasp so many notions that "what part of this aren't you getting? Er, core concept" became a running gag in the show. Whilst unable to grasp a number of basic concepts related to his job he is nonetheless a competent idiot.
 * He was simply unable to grasp that a rigid airship filled non-flammable helium was considerably safer than, say, the Hindenberg.


 * The Veggie Tales silly song "The Pirates Who Don't Do Anything" features Pa Grape singing about never steering ships, Mr. Lunt about never swabbing poop decks, and Larry about never throwing his mashed potatoes up against the wall. Pa and Mr. Lunt try to explain to him that "we're supposed to sing about pirate-y things", but get sidetracked into a debate on whether Pa looks like Cap'n Crunch. Larry sings another gleefully un-piratey verse and Pa shakes his head and proclaims "you just don't get it" before the song ends.
 * Averted in an episode of Futurama. The Professor shows everyone a complex equation. Amy gasps as she realizes it describes the impending end of the world. Then Hermes reacts as he realizes what it means. Fry just says "Don't wait for me."