Bob is acting unusually. Maybe he knows something he shouldn't or is spouting highly advanced facts about nuclear physics in Latin. The leading theory is extraordinary maybe he's possessed, or maybe his Evil Twin has taken his place. Someone will propose a mundane alternative like, "He read a book about it". Everyone rejects it out of hand because it would be out of character for Bob, and they return to the extraordinary theory.
This mostly occurs in Speculative Fiction. It serves to reinforce our characters' comfort with the extraordinary while simultaneously reinforcing characterization. The rejection will frequently be nonverbal, consisting instead of "Are you crazy?" looks.
Bonus points if said mundane explanation actually is the explanation.
Note that not every case of characters choosing an extraordinary explanation over a mundane one is this trope. This is only if the mundane explanation is rejected out of hand because it would be completely out of character for said person.
Related to Arkham's Razor, which is where the weirdest solution is most likely to be the true one.
See also Grail in the Garbage, where the valuable and/or powerful object was found in a ridiculously mundane place because no-one thought to look there.
- In H. P. Lovecraft's "The Alchemist" men of the narrator's family all die at the age of 32, supposedly due to a curse laid on the family by the son of an alchemist one of his ancestors killed 600 years ago. While researching the curse, he dismisses the possibility that his ancestors were assassinated by descendants of the alchemist, but it turns out that the alchemist's son has, in fact, been murdering them by assorted means over the centuries. This entails him having invented an elixir of immortality so that he could stick around and see the job done, so it's not an entirely mundane solution.
- Dirk Gently does this to some extent in The Long Dark Tea-Time of the Soul. When he meets a girl who constantly recites the previous day's stock quotes (in real time, just with a 24-hour delay), he rejects the assumption that she's just memorizing them somehow (after all, the information is out there!) in favor of some more mystical explanation, because nobody would ever go to that much trouble. It's a little different since he's arguing on the basis of general human nature, not the specific character, but the principle is the same. Dirk sums this up by reversing Sherlock Holmes' usual maxim: Eliminate the improbable, and whatever remains, however impossible, must be the truth.
- At the climax of Cold Days, Harry Dresden faces off against another hero, Fix, set on him by one of The Fair Folk, who told Fix that Harry was the villain. After getting his butt thoroughly kicked, Harry sums up the situation thusly: Either a being who Cannot Tell a Lie has, or Harry Blackstone Copperfield Dresden is an evil mastermind. Faced with the evidence, Fix realizes he's been used.
- The Stargate SG-1 episode "Window of Opportunity": Jack has prior knowledge of a briefing Carter is giving, and claims that he's remembering things from the future. Carter suggests, "Maybe you read my report?". Daniel gives her a look and repeats, "Maybe he read your report?" as if it was the most ludicrous suggestion. Everyone else (O'Neill included) seems to agree. Even Carter's tone as she says it suggests she thinks it's highly unlikely.
- Buffy the Vampire Slayer
- The gang is attempting to contact Buffy:
Xander: Well, she didn't go home. I let the phone ring a few hundred times before I remembered her mom is out of town.
Giles: Well, maybe Buffy unplugged the phone.
Xander: No, it's a statistical impossibility for a 16-year-old girl to unplug her phone.
- There's also the time that Xander was possessed by a hyena. Buffy quickly figured out he was possessed while Giles believed he was just being a teenage boy. Knowing Giles' teen years, this assumption makes a bit more sense.
- The gang is attempting to contact Buffy:
- Played with in Dexter, when Astor asks what Lumen is doing in Dexter's house. Dexter claims they're not dating, and she's just a tenant. While she's much more than that, Dexter never lied. They aren't dating at this point.
- An episode of NYPD Blue had the detectives come across a murder scene with multiple victims, all of whom were naked prior to being killed. The detectives offer increasingly bizarre theories as to why all of the victims were naked, with most of the theories being sexual. They eventually question a person who had escaped the scene before the murders, and she explained that the people were packing drugs for a local gang, and they were naked because "No pockets" ie, so the people doing the packing could not steal any of the drugs for themselves. All of the detectives are chagrined by this obvious (and non-sexual) explanation.
- On Two and a Half Men, Evelyn Harper steps in to fund her grandson Jake's college expenses. Jake's dad, Alan, finds himself losing his drive, first losing interest in his job, and then expressing a very real fear that he may commit suicide. This provides the Eureka Moment for Alan's brother Charlie, who had been trying to figure out why Evelyn is behaving uncharacteristically. Alan briefly refuses to believe this, until:
Charlie: Okay, let's look at the alternate explanation. For the first time in her life, our mother is being totally selfless and thinking about someone else's well-being.
Alan: Dear God, my own mother's trying to kill me.
- Smallville does this with Clark's glasses. Everyone has always assumed that Clark Kent wore glasses as part of his disguise. The truth is that he received an injury that made him far-sighted: he actually needs them to read!
- Umineko: When They Cry: Cardboard boxes and Small Bombs. Trying to find a Possible Mundane Solution seems to be how Battler can win.
- Ace Attorney Investigations: In the first case, the master key to the High Prosecutor offices went missing in the presence of Maggey Byrde, who was convinced that it was stolen and later returned. When Edgeworth posited the theory that the key had simply been misplaced in that time, Maggey and Gumshoe dismissed that idea, as her luck didn't run that way. She was right; turned out the key was indeed stolen.
- Freefall has some fun with this. Apparently, Florence is a vampire. Either that, or she really swam in the cold water a bit too long.
- In The Order of the Stick, there are five Gates keeping an Eldritch Abomination called "the Snarl" contained. The paladins of the Sapphire Order are responsible for guarding one of them. However (due to disagreements on behalf of the people who established them), they all swore an oath not to look into the status or even location of the others. The villains find this difficult to believe, to say the least.
Redcloak: I find it far more probable that you are somehow resisting my magic. This "Soon's Oath" story is just that — a cover story designed by your leaders. [...]
O'chul: You find the idea that I have some sort of secret knowledge implanted in my brain by the elders of the Sapphire Guard that has been so deeply suppressed that no magical effect can unearth it to be simpler...than the idea that I just don't know anything?
Redcloak: I liked the way I phrased it better.
O'chul: No doubt.