Entertainingly Wrong

When somebody comes to a completely logical conclusion from what they know, and are completely wrong.

The reasoning is usually (although not always) completely logically Valid, but either one of the premises is wrong, there exist things outside the frame of reference of the deducer, or there are just plain facts not in evidence that cause the wrong conclusion to be reached.

A common feature of rational Wrong Genre Savvy characters who don't think they're in a story, or Master of Delusion characters.

Inverse of Right for the Wrong Reasons. Many examples of Sure, Let's Go with That and Future Imperfect are the result of the assuming party being Entertainingly Wrong.

Anime and Manga

 * Rosario + Vampire pulled this with Tsukune's older cousin, she came to perfectly valid conclusion considering she didn't know about monsters being real prior to her arrival. Of course she was clearly not being entirely observant seeing as a succubus transformed right in front of her, a snow demon froze a goldfish in an unobscured line of site before her and a witch' magic kept dropping amusing weights on everyone that tried to talk to Tsukume
 * That and a faerie like spirit came right out of the cursed mirror she was holding, and she was still in denial till All Hell broke loose at the Extranormal Institute she was visiting
 * In One Piece, upon learning that his friend and leader is also the father of Monkey D. Luffy, Emporio Ivankov makes the perfectly valid assumption that Luffy's brother Ace is also the son of said friend and leader and assists Luffy in a jailbreak to save Ace from certain death. Revealed only after the jailbreak is.

Comic Books

 * There's a moment of this at the conclusion to Batman R.I.P. Batman concludes that the Joker's playing card suits were a reference to the red and black poisoned flower petals used against Batman during the climax. They weren't. There was no clue, the Joker was addressing Batman's skill at solving these kinds of things by providing a riddle with no answer. The Joker's crazy, you can't expect him to be honest all the time.
 * In a comic based on Batman the Animated Series Riddler manages to deduce that Batman has to be a rich Gothamite with a personal grudge against crime. He proceeds to accost a roomful of suspects matching the criteria. Bruce Wayne is not among them.

Fan Works

 * In chapter 15 of Inviolate, Lex Luthor concludes that Bruce Wayne is backing Batman... but thinks that Batman is Matches Malone (sort of true, since both are really Wayne), and that Harvey Dent wore the cowl before him (completely false, but sensible - Jim Gordon thought much the same thing at one point).
 * The premise of No Place Like Eureka, a Buffy the Vampire Slayer/Eureka crossover fanfic, is that Dawn gets embodied in Eureka rather than Sunnydale, using Carter and Stark's DNA instead of Buffy's. When the Eureka residents realize that something is strange about Dawn, they come to the perfectly logical—and entirely wrong—conclusion that she was born in the future and sent back in time for some inscrutable reason. Hellgods and mystical Keys aren't really on their radar...
 * There's a lot of this going around in Taylor Varga, a Worm/Luna Varga crossover fic:
 * PHO's first collective guesses about the nature of lizard girl cape Saurial (actually Taylor Hebert) are (mostly) wildly off-base, but Taylor decides to embrace them and run with them, in the process creating The Family and its "history" that predates the Dawn of Man.
 * Similarly, the PRT's initial attempts to figure out the Family. Followed by their erroneous but perfectly reasonable "discovery" that they're extraterrestrials, thanks to genetic evidence planted by Amy "Panacea" Dallon.
 * The conclusions a pair of deliverymen from New Jersey, dropping off non-lethal munitions provided by a Hebert family friend who is an actual mob boss, make about just what's going on at the DWU. This is subtly encouraged for his own amusement by the head of DWU security, and another union member's insistence on addressing Danny as "padrone" certainly doesn't help.  And then the drivers overhear a conversation between Alec and Brian where Alec boasts of getting a headshot on someone in the unspoken context of a video game.  The drivers leave with a lot of misconceptions about the DWU and Brockton Bay.
 * It stops being "entertaining", though, when thanks to some Idiot Ball-holding, a number of law enforcement agencies come to similar conclusions and start trying to infiltrate the DWU so they can bust the "smuggling" and "money-laundering" operations they are sure have to be going on there.
 * Vicky "Glory Girl" Dallon, trying to figure out the connection between Saurial and Taylor, eventually concludes the two were raised together when, thanks to Taylor's recently-acquired ability to be in two places at once, both she and Saurial attend a study session.
 * Similarly, Sophia "Shadow Stalker" Hess concludes that Taylor and Saurial had to have known each other for years, based on videos of how easily Taylor took down a would-be car-jacker, and that Taylor had to have let herself be bullied at Winslow as part of a Long Con.

Film

 * The entire plot of Hot Fuzz is this. Nicholas Angel examines the evidence he has uncovered and deduces that everything that has been going on in town is all part of a master scheme involving real estate prices. The truth is much sillier....and much more twisted and evil.
 * Norrington in Pirates of the Caribbean: Curse of the Black Pearl refuses to interrogate Jack Sparrow about where to find the pirates who attacked Port Royal and kidnapped Elizabeth. The pirates who attacked left Sparrow in his jail cell, therefore they weren't his allies, and so there's no reason to think that Sparrow knows where they went. In any case, Norrington wouldn't trust a pirate's word anyway. Norrington's conclusion was wrong because there were certain facts that he couldn't have known (they weren't his allies, but they were his old crew and were in fact his enemies, and he did know where they went). So Will takes it on himself to spring him and go after Elizabeth himself.

Literature

 * The Discworld novel Men at Arms pulls one of these on the reader (and Corporal Carrot). We're introduced to Angua, a new female recruit to the Night Watch, very much a Boy's Club. Both Vimes and Colon complain about her being the worst of the new recruits brought in to diversify the Watch, because she's "a w--" before being interrupted by an explosion. As it turns out, they're not complaining about her being female, but about her being.
 * Motel of the Mysteries by David Macaulay is all about future archaeologists getting present-day America entertainingly wrong.
 * Happens in the Harry Potter series, most prominently in Harry Potter and the Half-Blood Prince and Harry Potter and the Deathly Hallows. In Half-Blood Prince, Dumbledore and Harry both come to the perfectly valid conclusion that Voldemort had tried to get a job at Hogwarts in an attempt to get ahold of an item belong to a Hogwarts Founder for use as a Soul Jar. In Deathly Hallows, Harry realizes they had it backwards, and that Voldemort used the interview to hide one of his Soul Jars in a hidden room on the way to Dumbledore's office. Actually getting the job would've just been a bonus.
 * In The Salvation War, the demon lord Belial was extremely confused about why the humans were slaughtering the demonic hordes even though they used to only cower in fear a "mere" five millenium ago. He thought to his own forges, and how his slight refinements to tridents made them much better. He came to the conclusion that humans had been so scared of the mighty demons that they stockpiled all many great weapons and only use it now that they faced extinction. Wrong, sure, but much closer to the fact than the rest of Hell assuming that humans suddenly have magic.

Live-Action TV

 * In the Stargate SG-1 episode "Arthur's Mantle", Dr. Lee knows that Sam and Cameron were in a room with an Ancient artifact; that the security cameras in that room went out and when they came back on the two of them were no longer visible; and that the cameras in the hallway outside the only exit don't show them leaving the room. He concludes that the artifact must have miniaturized them and spends quite a bit of time trying to find them on the floor of the room. In reality, it made them invisible and intangible, and Sam spends most the episode hovering over Dr. Lee's shoulder, in frustration with the fact that she can't communicate this to him.
 * Commonly seen in the Law & Order franchise when one or more of the initial, red-herring, suspects turns out to have a perfectly reasonable explanation for their suspicious behaviour. The guy with the shrine to a dead kid who was stalking him, who quit a high-paying job to work with young children, all seeming to perfectly fit a predatory pedophile? The kid's real father concerned about his care by the adoptive parents and wanted to be close to him.
 * Also seen in Criminal Minds when an initial profile ends up being wrong and they're forced to re-evaluate the entire motive (and suspect). Often the result of Pulling the Thread.

Tabletop Games

 * From Forgotten Realms: The history of High Moor. One pissed-off druid in Elminster's Ecology assumes it to be the result of typical human deforestation. It's the result of a Killing Storm. He just assumed based on what he saw and knows, and probably never saw a single elf capable or willing to do this, nor would know, since elves aren't eager to tell anyone else about less glamorous moments of their past.

Theatre

 * In My Fair Lady, the rival dialectitian picks up on all the clues that Eliza's perfect English is the product of coaching, but he assumes that her manners are innate, and thus concludes that she's a foreign aristocrat instead of that she's a lower-class Englishwoman.

Video Games

 * In Batman: Arkham Asylum, the Riddler is convinced that Batman is a Villain with Good Publicity; he must be stealing money from criminals he catches to fund his Wonderful Toys. Besides his mistaken belief that "no one is that selfless", he doesn't know that Bats is legitimately filthy rich and has an R&D department he can nick stuff from.
 * In a wall-breaking moment, should the player solve enough of the Riddler's riddles, he'll scold 'Batman' for looking them up on the internet. It becomes Entertainingly Wrong for those players who resisted the temptation to "cheat." Many players do resort to solving puzzles by looking them up.

Web Comics

 * At one point in Homestuck, Terezi comes across the scene of 's recent killing spree. Having just seen   after he was impaled by , she concocts a crazy sequence of events positing   as the killer there as well... except she immediately realizes it makes no sense.
 * In Kaspall, Sam concludes that the world would be a lot better if it was just humans, because there would be no Fantastic Racism.
 * Banquo in the second Hark a Vagrant strip on this page.
 * In Narbonic, Dave's internet girlfriend Lovelace (who is actually Professor Madblood's supercomputer) lets slip that she's staying in the same hotel room as Madblood at a convention. When Dave and Helen break into Madblood's room to find her, they discover only one set of luggage; Dave mistakenly concludes from this that Lovelace is Madblood.
 * Similar to the Kaspall example, in one Order of the Stick comic, Roy concludes that if there were no raise dead or planeshift spells (meaning death was permanent, and you didn't even know for certain there was an afterlife), nobody would have wars.
 * In Freefall Varroa Jacobsoni from company that performs terraforming investigates the case of a killed deer.

Web Original

 * In the early stories of the Whateley Universe, Phase brilliantly deduces that the person who left him an extortion note just before school starts is... Assistant Administrator Amelia Hartford, who has a grudge against Phase's older sisters! Phase is so, so wrong. But he doesn't figure that out for about a month, when he spots the real clue and realizes what it means (which is probably a correct series of deductions).

Western Animation

 * In The Batman, a couple of far-future archaeologists who are excavating the Batcave have a few conclusions like this. They think Oracle's wheelchair belonged to Alfred, for example, and after seeing a portrait of the Wayne family (Bruce and his parents), they conclude that Thomas Wayne was Batman, and Bruce was Robin.

Real Life

 * An example of It Will Never Catch On from Real Life: someone predicted television would never be successful in the United States because "Americans don't have the attention span to sit and watch a box for an hour". Logically sound, but based on wrong assumptions.
 * A lesser known real life example occurs when Atahualpa, the last Inca emperor, hears about the Europeans approaching the Inca capital of Cuzco. Based on reports of these foreigners wearing helmets, he comes to an astonishingly brilliant conclusion had he only known about European warfare. He notes that the Europeans have cooking pots (metal helmets for protection) over their heads. Atahualpa believed that anyone who wore cooking pots was crazy, which goes double if said people didn't even use those cooking pots for preparing food!
 * Imagine his Oh Crap reaction when he set an ambush in the capital with thousands of soldiers vs. slightly over 100 Europeans, only to have said helmets turn out to be armor making them nigh-impossible to kill with Inca weaponry. The diseases the Europeans carried only cranked it Up to Eleven.