Bob is a dyed-in-the-wool Agent Scully. No matter what Alice tells him, he cannot accept that the truth is anything other than what his own common sense and experience tells him. Usually Alice, the hero, gets about as fed up as she can get with Bob, because Alice knows the truth and Bob. Will. Not. Listen. But then Bob runs into the monster, and suddenly finds that he can no longer pass it off as swamp gas from a weather balloon that was trapped in a thermal pocket and reflected the light from Venus. This shocks Bob into dropping the Idiot Ball very quickly, and very heavily.
Often Played for Laughs, since the former skeptic is almost always the most rational denier up to this point. Bonus points are given if the skeptic is also an Obstructive Bureaucrat who suddenly comes to his senses. This sort of occurrence also helps to kick the action along since now they can treat it as Serious Business. If they're unlucky, they might have caught a Contagious Cassandra Truth. Compare Skepticism Failure and Horror Struck.
- Kyon from Haruhi Suzumiya initially thinks he's the Only Sane Man after Nagato, Mikuru and Itsuki tell him the truth about their nature as well as Haruhi's. Then, Ryoko tries to stab him, traps him in a sealed dimension, turns her arms into energy tentacles, then Nagato arrives, survives getting impaled by twenty spears, chants a couple of spells, and Ryoko dissolves. Needless to say, he's afterwards quick to believe in whatever he sees or hears from these three.
- Chisame in Mahou Sensei Negima! goes from the Only Sane Man into... the only sane man aware that the universe she lives in doesn't make sense at all but whatever. She gets cool age changing pills and magic hacking powers if she plays along, right?
- In earlier parts of One Piece, Zoro says that he doesn't believe in dragons. Later on in Punk Hazard, when he and the crew meets an actual dragon, he's visibly surprised.
- Seto Kaiba spends much of Yu-Gi-Oh! ranting against "Egyptian fairy tales" and "hocus-pocus magic" whenever weird things happen, especially involving Yugi and Yami/Atem fighting to save the world from various supernatural threats. By the end of the series, though, he finally accepts that all the weird stuff is real, including the nature of Yugi and Atem's relationship. It's to the point that in Yu-Gi-Oh! The Dark Side of Dimensions, Kaiba actively seeks to resurrect Atem for one more duel.
- Whenever The Phantom start fighting crimes in the City, there will always be a black mook that start pull one and one together and then says a variation of "The Phantom! Grandfathers stories were True", this giving him a chance to inform the White Crime Leader what's up only for it to be dismissed as "Silly Jungle Stories".
- In Redaction of the Golden Witch, the adults of the Ushiromiya family decide that Kinzo's rantings about magic and witches might not be so far-fetched after all. In fact, they're willing to try working Black Magic themselves in order to solve their problems, and bring Kinzo back via Human Sacrifice.
- Sansa in the A Song of Ice and Fire/Iron Man crossover A Man of Iron initially blows off the stories about Iron Man, since the scarcity of magic in Westeros makes a flying knight with magic beam weapons all but impossible. It's only when Ned confirms that the stories are fact that she becomes a big fan of the guy.
- In Scooby-Doo on Zombie Island, the gang has spent so much time busting fake monsters and other weirdos that when strange things start happening, they don't immediately accept that it really is supernatural this time. Fred, in particular, seems determined to play Agent Scully when they run into the zombies—until he pulls one of their heads off. And the zombie reattaches it. The denial vanishes very quickly. From that point in the franchise, Velma is the only one to retain having skepticism about the supernatural as a character trait, with one movie making her need to never become this trope a part of her backstory.
- Mike Enslin in 1408 is a professional skeptic who makes it his life's work to go around reviewing supposedly haunted locations. When he checks into the Dolphin Hotel's titular room 1408, against the urging of virtually every single member of the hotel staff, he learns very quickly how much he screwed up.
- The marines in Aliens are pretty much uniformly contemptuous of Ripley's description of the xenomorphs at first, refusing to believe that they could be as effectively lethal as she was saying. After all, they are rough, tough hardcore marines. Suffice to say they believe really quick after facing off against the creatures.
- Captain Lorenzo in Die Hard 2 believes John McClane that Colonel Stuart and Major Grant are working together only after McClane empties a submachine gun (the same kind used by the soldiers in their attack against the terrorists) full of blanks at him. Lorenzo then calls in the cavalry.
- From Dusk Till Dawn: The fact that vampires are real comes as a shock to everyone... but they get over it quickly.
- In The Sixth Sense, Doctor Malcolm Crowe believes that Cole Sear's problems stem from some sort of schizoaffective disorder... until he encounters something that turns his skepticism on its head.
- In Split Second, Detective Dick Durkin refuses to believe that the Serial Killer he and Harley Stone (his partner) are tracking isn't actually a human being at all, but rather some kind of monster. And then he runs face-to-face with the thing.
Stone: Did you see him?Durkin: That wasnae a him, that was a fucking it!
- Seeing the monster also leads to Durbin's line, "We need to get bigger guns!", which under the circumstances was a very rational reaction.
- Sarah Connor starts the first film only knowing that there is a Serial Killer hunting down women with her name all over Los Angeles, and is completely unable to believe Reese's story (she even tries to run away a couple of times while he's saying it, even after he saved her life when the Terminator tried to kill her. The fact that Dr. Silberman labels Reese as a complete nut job and the cops theorize that the Terminator is wearing body armor and may be on PCP also keeps her on the skeptical side for a little while longer). By the time the Terminator finds her again and slaughters its way through a police station single-handedly, she is a total believer and by the time of Terminator 2, she has taken all the measures she could to prepare herself and John for the Robot War ahead and tried to do some damage to prevent Skynet from becoming a threat... which, quite understandably, landed her in an insane asylum.
- The arcs of both John Connor himself and Miles Dyson on Terminator 2: Judgment Day are to consider that Sarah is a complete loon and what she spouts isn't real (and John, who grew up around her, is pretty bitter about it) but they immediately come around when they encounter the Terminators.
- Doctor Peter Silberman encountered proof that Sarah Connor wasn't crazy in Terminator 2: Judgment Day. By Terminator: The Sarah Connor Chronicles, he's living in isolation, away from major cities, raising dogs and keeping a healthy sense of paranoia about killer robots disguised as human beings. He even apologizes for not believing in Terminators, not that it does him much good.
- However, this isn't the case in movie continuity. He appears in Terminator 3: Rise of the Machines, as Scully as ever, and ascribes his experience with Terminators to psychological trauma (before recoiling in fear at the sight of the Terminator showing up again).
- Oh, come on, Indiana Jones. In Raiders of the Lost Ark he remarked that despite being an expert on the occult he doesn't believe in magic, superstition, (and in Indiana Jones and the Kingdom of the Crystal Skull, aliens.) yet in Raiders and Skull he believes it enough to get the hell out of there and or not look at the item that would have killed him.
- In The Woman in Black, Sam Daily finally acknowledges the supernatural nature of the house and the existence of the ghost in the last act, and helps Kipps lay the ghosts to rest. Well, he tries...
- In The Haunting (1963), Luke Sanderson is flippantly skeptical that anything supernatural is going on at Hill House, no matter how creeped out the rest of the cast (and the audience) is getting. But by the end of the movie, even he has given in, declaring that the house ought to be burned down and sown with salt.
- In Cat People, Oliver doesn't believe in the story of cat people Irena tell him about. At the end of the movie, when he finds her body shapeshifted into a panther, he realizes how wrong he was.
- Pirates of the Caribbean:
"You best start believing in ghost stories, Miss Turner... you're in one!"
- In Pirates of the Caribbean: The Curse of the Black Pearl, Miss "Turner" (actually Miss Swan) tells Captain Barbossa she doesn't believe in ghost stories. She then sees the crew by the moonlight and discovers that the ship she's on (The Black Pearl) is crewed by the undead.
- In Pirates of the Caribbean: Dead Men Tell No Tales Carina Smythe, being a stalwart woman of science, finds the concept of curses and ghosts absurd. It takes coming face to face with a crew of cursed undead to change her mind.
- In the Star Wars franchise, contrast Han Solo in A New Hope and again over thirty years later in The Force Awakens:
Han (younger, ANH): Kid, I've flown from one side of this galaxy to the other, and I've seen a lot of strange stuff, but I've never seen anything to make me believe that there's one all-powerful Force controlling everything. 'Cause no mystical energy field controls my destiny. It's all a lot of simple tricks and nonsense.
Han (older, TFA): I used to wonder about [the Jedi] myself. I thought it was a bunch of mumbo jumbo. A magical power holding together good and evil, the Dark Side and the Light? The crazy thing is... it's true. The Force. The Jedi. All of it. It's all true.
- Fright Night (1985). Peter Vincent did not have faith in God, so when he tried to use a cross against the vampire Jerry Dandrige it didn't work. Let's just say that the next time Peter puts a crucifix in Dandrige's face, after Peter has killed a vampirized Evil Ed, it turns out very differently for Dandrige.
- In Doctor Strange (2016), Strange quickly comes around to the "magic is real" camp after The Ancient One shows him a thing or two. (Such as punching his astral form right out of his body.)
Strange: Teach me...
- A skeptical atheist walks around near Loch Ness. Suddenly, the Loch Ness monster erupts from the water and grabs him. In panic, he shouts "Oh Lord, save me!" God answers: "You dare to ask me for help, when you didn't believe in Me one minute ago?" The atheist says: "Have mercy, Lord - one minute ago I didn't believe in the Loch Ness monster either!"
- Paksenarrion, from Elizabeth Moon's The Deed of Paksenarrion, gradually changes from a skeptic to a believer to a full-blown Paladin of St. Gird; the Girdish medallion Canna left to Paks when Canna died gives the first signs when it starts warning Paks of dangers.
- At the end of Victory of Eagles, General Wellesley declares himself a convert to the idea that the Dragons of the Aerial Corps are in fact fully sentient... then declares that he will be "damned if I will let you make them political" and manages to get convicted traitor William Laurence's sentence of death commuted to Transportation to Australia on the condition that he take the most obvious prospective rabble-rouser (Temeraire himself) with him.
- In Man from Mundania, Grey Murphy refuses to believe in magic after being brought into Xanth, until he encounters a river flowing up a cliff and simply can't come up with a scientific explanation for it. It helped that his magic talent was Anti-Magic, so he kept unconsciously nullifying magic near himself, such that some of the things Ivy tried to show him didn't work.
- Professor Summerlee in The Lost World (1912).
- Word of God stated that Cloudtail and Mothwing of Warrior Cats stopped being atheists after an army of dead cats invaded the Clan territories and a second army of dead cats helped the Clans in The Last Hope. In later books (that were not planned at the time of the statement) it is shown that Mothwing actually still doesn't believe in StarClan.
- Dr. Claymore from the Percy Jackson and the Olympians short story "Son of Magic." Then again, being attacked by Lamia and befriending a son of Hecate will do that to you. Not to mention dying, meeting a goddess, then coming back to the mortal world as a familiar.
- In The Sanguine Chronicles, Marko's friend Janie is a hardboiled skeptic when it comes to the supernatural. Then she discovers Marko is a werewolf/vampire hybrid when she catches him mid-shift.
- In the original Dragon Lance trilogy this applies to pretty much the whole world. The gods stopped responding to prayers and providing clerics with powers after the Cataclysm. Centuries later at the time of the books, the gods have been largely forgotten and even those who remember their names consider them to be myths. The same applies to dragons which haven't been seen for even longer. Events quickly convince everyone that both the gods and dragons are very real.
- Dracula: Two examples of this
- Harker at first thinks the village is just being superstition despite being an outsider to Transylvania (though they don't really tell what the danger is, just that it's a really bad idea to go to Dracula's castle). But after meeting the count, finding how strange he and his dwelling are and ultimately nearly being bitten by his vampire brides, it doesn't take long for him to become a believer.
- Later after Lucy dies from Dracula succeeding in draining her blood, Van Helsing tries to convince Seward, Arthur and Quincy that she will become a vampire and be a danger to all. Naturally they think he's coo coo, So Van Helsing decides he needs to show them first. He starts with Seward, his trusted student, as they watch Lucy's coffin and indeed find it initially empty then after waiting a bit, find it filled again with her body, only to discover she hasn't decayed since she was interred and in fact much more beautiful then ever. The following night, Van Helsing gathers the rest of the men and confront Lucy directly as she prowling the night. Indeed, seeing her bearing fangs with bits of blood on her lips, acting not at all like the Lucy they know (feral and seductive instead of kind and caring), acting fearful of a cross and using her powers to flee back to her coffin is more then enough proof to the men that vampires and the threat they pose are real.
- Game of Thrones: Growing up in the Crapsack World of Westeros, and especially his family, made Tyrion a cynical man and so he never had any faith in anything even himself. However after meeting Daenerys and seeing the wonders she can do Tyrion admits to her that he now believes in her and her vision for the future. When he meets Jon Snow again in Season 7 he even admits that he now believes his tale of White Walkers when the Tyrion of the first season sarcastically referred to the things beyond the Wall as "Grumkins" and "Snarks".
- In the How I Met Your Mother episode "Matchmaker" Marshall and Lily (both a bit superstitious) are convinced their apartment is infested by a mutant combination of a cockroach and a mouse (which they dub a cockamouse). Robin plays the role of skeptic until the end when she finally sees the cockamouse herself (though we never do), and it's revealed that somehow the cockamouse can fly too.
- In The X-Files, Dana Scully, originally the hard core skeptic of the dynamic duo, became the believer (with her new partner, Agent Doggett, who took the role of the skeptic) when Fox Mulder was Put on a Bus.
- Lost's Jack after he returned to the Island. Previously he denied everything supernatural or odd, even if it happened right in front of him and other people saw it. Once he became a believer, he went to the opposite extreme-believing everything. Such as lighting dynamite right next to him on a slight chance that he can't die...
- On Supernatural Agent Henriksen spent most of his time ruthlessly pursuing Sam and Dean, whom he believed to be serial killers with psychotic delusions. Seeing a mass outbreak of demonic possession up close changed his opinion on a lot of things, and he chose to help them. Sadly he was killed in the same episode.
- Emma Swan of Once Upon a Time initially did not believe that The Evil Queen from Snow White had cursed a bunch of fairy tale characters to be trapped in our world. Seeing Henry fall unconscious with no apparent cause and subsequently fighting Dragon Maleficent disabused Emma of her skepticism.
- Zak Bagans, the leader of the Ghost Adventures crew, is the one who has the best time relating to skeptics they encounter during investigations because he himself used to be a total skeptic when it came to the ghosts and the supernatural. In the original opening for the show, Zak explains that he never believed in ghosts until he came face-to-face with one—in Zak's case, it was the ghost of a woman who had committed suicide in an apartment complex that he once lived in while residing in Michigan. Ever since then, Zak's become investigator of the paranormal.
- Throughout the first two seasons of Star Trek: Enterprise, T'Pol refuses to even entertain the possibility of time travel, simply because the Vulcan Science Directorate has declared it impossible. Then in season 3, she and Archer are sent back to 21st century Detroit; from then on, she's far more accepting of time travel.
- Clive Barker's Undying: Patrick started his career as an Occult Detective trying to "debunk folklore and mysticism." Presumably he stopped trying to disprove the supernatural at the latest by some point between obtaining the clearly magical Gel'ziabar stone and gaining a German wizard as an archrival.
- In Alan Wake, Sheriff Breaker spends most of the time thinking that Wake is having a mental breakdown, and doesn't believe his stories of shadowy attackers and monsters. And then Agent Nightingale is stolen by the darkness right in front of her. One of the first things she says after she witnesses Nightingale's death is "Tell me how we can stop these things" with no hesitation at all.
- Girl Genius: Carson Von Mekhan, the former seneschal of Castle Heterodyne and secret ruler of Mechanicsburg during his masters' long disappearance, was of course initially dubious of Agatha's claim of being the real Heterodyne heir. Seeing Agatha in action wore down his doubts, and they were banished completely when she made the kill-happy Castle Heterodyne back down from killing Herr Diamant for doubting that there even was an heir.
- Vanamonde, his grandson and successor, was dispensed from skepticism even earlier, once he had a sip of Agatha's special coffee brew and had a coffee connoisseur nirvana moment. And then he wouldn't shut up about the "perfect coffee".
- Homestuck: We see in some flashbacks that the Kids have been getting contacted by the trolls periodically throughout their lives, but they've never believed that the trolls were anything other than... well, Internet trolls. When the Sburb session starts up and they get transported into the Medium, and all the other weirdness that happens, they are suddenly much more inclined to believe what the trolls have to say.
- Stand Still, Stay Silent: One of the storylines is the Odd Friendship between Flat-Earth Atheist Emil and mage Lalli. At the end of Chapter 16, Lalli ends up needing to use magic right under Emil's nose, which shows Emil that not only does magic exist, but the "mage" on Lalli's resume was not just some kind of fancy non-literal title.
- Captain Black of Jackie Chan Adventures gets this in the Season One Finale. He becomes so convinced in fact that in later seasons he is often seen as mentally unstable by his superiors for constantly mentioning magic and demons.
- Happens to Eduardo in the first episode of Extreme Ghostbusters. His very first line is "Ghosts. Yeah, right." Then Slimer shows up, and by the end of the episode, Eduardo is a Ghostbuster.
- My Little Pony: Friendship Is Magic: In "Feeling Pinkie Keen," Twilight Sparkle is dismissively skeptical of Pinkie Pie's "Pinkie Sense," even though Applejack (who has lived in Ponyville a lot longer that Twilight) confirms that it's real. At first she insists that Pinkie's ability to predict certain events just before they happen is nothing but coincidence. Then she tries to analyze how the Pinkie sense works, because (as Pinkie points out) Twilight can't believe something she doesn't understand. After being repeatedly smacked in the face by compelling evidence, Twilight accepts that the Pinkie sense exists, even though she can't explain it.