This is a common plot device often used to kickstart a story, or get it into high gear.
Basically, the heroes discover that some bad guy is up to no good. The problem is that for whatever reason, the hero has trouble getting people to believe him. Maybe because the hero is a kid, because the bad guys are respected authority figures, or because their scheme sounds outlandish. They may have tried to deliver a warning without getting evidence first and been dismissed out of hand. Or maybe the authorities do believe them, but can't act without evidence. Either way, the heroes need proof of what the bad guys are doing in order to get anyone to believe them, and the ensuing adventure becomes essentially about that. Of course, this plot isn't quite able to catch up in this day and age of hand-held phone recorders/cameras/camcorders in cell phones; because that would get in the way of the drama of trying to acquire evidence. Often they'll come up with different ways of recording information that's complicated enough for the plot.
This is also a way to get otherwise reluctant heroes involved in the plot. If for no other reason than the fact that since they can't convince anyone else, it's all up to them to solve the problem.
- The main obstacle for L of Death Note is not in deducing Kira's identity, but in finding proof beyond a shadow of a doubt to support his deduction. Not unreasonable, given that Kira is using a magic killer notebook to commit his crimes. Without proof, who would believe that?
- What Tenma of Monster occasionally tries to do about Johann. The rest of the time he's attempting to kill him.
- A large part of Red River (1995): Kail and his group know that Queen Nakia is behind about 90% of the bad things that happen in the story, but she is very good at covering her tracks, and you don't accuse the second-most-powerful person in the Empire of serious crimes without some serious proof to back it up.
- A recurring hassle for Mickey in the Mickey Mouse Comic Universe before he can put a stop to whatever scheme he's gotten on the track of. Subverted in "The Mystery of the Robot Army!", where the police believed Mickey without further question but Mickey ruined things by taking a piece of evidence with him, which the villains discovered and took as cue that it was time to clear out before the police arrived. Lampshaded in "The Mystery at Hidden River" when Mickey discovers Pete's presence at the crime site early in the story:
Mickey: "Well, I don't have to be clairvoyant to know who's the villain in this mystery! The trick is to get the goods on him!"
- Dreaming of Sunshine: One of the reasons Shikako doesn't run around changing things willy-nilly is because no one would ever believe her. Instead she painstakingly begins investigating events of interest such as the Uchiha massacre, especially after being subjected to Tsukuyomi, and Akatsuki. This even makes sense, since she KNOWS the information is there and will thus notice things someone else would dismiss.
- This serves as the reason why Minato hasn't taken down Danzo yet in Catch Your Breath, despite knowing about his actions.
Minato: If I had any solid evidence to link Shimura directly to anything, Id have ordered the seizure of all of his assets within the village and put him under seal-enforced house arrest until we could have a trial.
- In Delenda Est, Harry might know what the dark lord is doing, but he cant tell Orion and Cygnus about it until hes got proof.
- Blue Diamond and Jasper do this on behalf of Hema in The Harvester when they are put on trial for being accused of a crime punishable by death, by bringing out Emerald as proof that they were framed.
- Tom says this almost verbatim about how they're going to clear Skinner's name in the fourth volume of The Private Diary of Elizabeth Quatermain.
- Many 1950s horror films used this plot device, specifically applied to teenagers (i.e. those who paid to see drive-in movies) who found out some horror or other, but the adults wouldn't believe them.
- This becomes the main challenge in Zodiac once the heroes become convinced that Leigh is the Zodiac. Despite mountains of evidence — the windbreakers, the gloves, the wing-walker boots, the knives, the guns, The Most Dangerous Game, the watch — it could all be dismissed in court as circumstantial.
- My Teacher Is an Alien starts off with Susan Simmons finding out that, well, look at the title. She knows full well no-one will believe her, and her efforts to try to get evidence are what set the story in motion.
- A Spy in the Neighborhood is about three boys who think a certain neighbor may be a spy. They want to get the cops on her case, but in order to do that, they need to find proof of some sort, so they basically spy on her.
- Jennifer the Jerk Is Missing starts out this way, as Malcolm needs her babysitter, Amy, to believe that he did indeed witness a kidnapping. They then try to prove it to the adults, which doesn't work.
- Animorphs starts off with the kids trying to expose the Yeerks' silent invasion to the world, in hopes that once the world knows what's going on, they'll be able to fight back. This plan becomes less significant as the series progresses, in favor of simple guerrilla war, but ultimately succeeds near the end.
- This happens in a few of the Alvin Fernald books by Clifford B. Hicks
- A major plot thread in Harry Potter and the Half-Blood Prince involves the titular character being certain that Goldfish Poop Gang leader Draco Malfoy is up to something, and trying (without success) to prove it. Of course, this is in large part due to the fact that the primary responsible authority figures (Dumbledore and Snape) already know he's up to something and want Harry to have as little to do with it as possible.
- Aiden and Meg of On the Run race to prove their parents' innocence when they happen to be arrested for a crime they didn't commit.
- In Babylon 5, several episodes involved a search for evidence to prove that President Santiago's death was an assassination engineered by his successor, not an accident.
- The Fugitive combines this with Stern Chase, as a wrongfully-accused man flees from the law as he tries to find the evidence to prove who the real killer was.
- The X-Files. If Scully had a catch phrase, "We need scientific proof!" would be it.
- Eerie, Indiana
- On Saving Grace, Rhetta is a forensic investigator and does all kinds of tests on any items that Earl gives Grace to prove his angelic existence. Boy, does she find proof.
- Subverted in Star Trek: Deep Space Nine. When Sisko sets out to find proof that the Dominion is going to attack the Romulans, resident spy-in-exile Garak tells him the best way to find it will be to manufacture it themselves.
- Happens a lot in White Collar. The criminals are often known right away; the trick is gathering enough evidence to allow the FBI to do anything about it.
- A common occurrence on CSI and its spinoffs. Often occurs on cases where the evidence isn't yielding as many leads as the CSIs need to make the case.
- About halfway through every episode of Monk, the titular detective will figure out who did it. Without exception, the person he accuses will have an airtight alibi (once, the guy was in space at the time of the murder), and Monk will have to find the one thing that doesn't fit.
- In 2 Gus must prove that Booth, his Evil Twin, exists in order to prove his innocence.
- The unaired Wonder Woman (2011 pilot) features this in a plotline. The police can't do anything to Veronica Cale without proof. Wonder Woman goes about this by stabbing a guy in the neck and hospitalizing him, getting negative results, torturing him in a bed, and then getting this confession thrown out because police can't use information gained from coerced testimony. Surely, the world's greatest detective.
- Hunter: The Vigil's Network Zero has proof of nearly goddamn anything. The problem is getting people to take it seriously.
- Not helping is that the same high-tech world they're relying on to break the news has some strict limits. Posting footage of a werewolf mauling someone on YouTube breaks its content guidelines.
- The early plot of Mass Effect revolves around the protagonist uncovering evidence to prove that the villain is actually the villain to the not-so-omniscient council of very visible politicians.
- Your first mission in Phantasy Star II is to recover a recorder from the Bio Systems laboratory in order to find out why the lab started making monsters. This is but the first step in proving that the Mother Brain is not as benevolent as she appears to be...
- In Baldur's Gate II you're required to find overwhelming evidence of the younger Roenall's wrongdoings, as all complaints about him have to go through...him. So you need something very convincing to convince his superior to break protocol and get rid of him.
- In the NES Dick Tracy game, as Dick is a by-the-book cop, you have to follow the trail and find a LOT of evidence before you can arrest any of the big villains, even though you can confront them directly at any time. Arresting them prematurely earns you a stern talking to from your boss. (Much to the chagrin of The Angry Video Game Nerd.)
- Kingdom Hearts: In Wonderland, Sora and company must clear Alice's name regarding an assassination attempt at the Queen and find evidence against the Heartless.
- In Beyond Good & Evil, this is basically the entire plot: to prove the Alpha Sections are secretly associated with the Domz they're supposed to protect against.
- In Fallout, after saving the mayor of a little town from an assassination attempt, he asks you to gather evidence on the person (a local crime boss casino owner) he knows is behind it. You can either side with the crime boss, pretend to be an assassin available for work to make him do an Engineered Public Confession thanks to a tape recorder the mayor gave you, or just plain bugging his room.
- In the first Gabriel Knight game, Mosely demands that Gabriel prove that the murders were committed by an actual Voodoo cult and that said cult is a threat to the public before he'll help Gabriel fight it.
- According to his introduction blurb, this is one of Kouji Tagawa's goals in investigating the mysteries of Shiokawa in World of Horror:
A picture is worth a thousand words. The government won't sweep this one under a rug.
- Zim of Invader Zim is a Devil in Plain Sight whose Paper-Thin Disguise shouldn't need any proof to expose, but the earth is largely populated by idiots so Dib is continually after "proof" (generally, a shot of Zim not in disguise) — he's managed to get it on more than one occasion, but since Failure Is the Only Option he always loses it even if he otherwise thwarts Zim's latest Zany-but-Evil Scheme.
- A common occurrence for Candace in Phineas and Ferb, despite the guys not being evil (at least not to us). Their inventions are always in plain sight, but their sister goes through great ordeals to actually get their mom to see it, resulting in this trope several times by using cameras etc.
- In the series Dragons: Riders of Berk, a series continuation of the movie How to Train Your Dragon, The Hero Hiccup knows the old man named Mildew not only destroyed the village's supply of weapons to defend the village and framed the dragons, he even saw the framing objects in Mildew's hut. But after Mildew destroys the evidence, Stoick explains to his son that while he really does believe, he can't punish Mildew for treason without hard evidence.
- The Deputy Dawg cartoon "Diamonds In The Rough" has the deputy tasked with finding a diamond smuggler, but the sheriff tells him not to make an arrest without evidence. A haphazard golfer swings by, and Deputy Dawg deduces that the golfer is the smuggler and the diamonds are in the golf balls. After he accidentally swallows some golf balls, Deputy Dawg is at the doctor with the golfer, and the X-ray shows the diamond-laden golf balls in DD's stomach.
- Gravity Falls: In the series premier "Tourist Trapped", Dipper worries that his sister Mabel is dating a zombie. Soos tells Dipper that unless he gets solid evidence, no one will believe his claims, leading to a montage of Dipper following "Norman" and Mabel on their dates. Dipper apparently gets his proof when he catches Norman's hand falling off and reattaching, goes to warn Mabel... And then it turns out that Norman is in fact a bunch of gnomes stacked up.
- In an episode of Stōked called "To Catch a Reef," Reef's accused of stealing various things from guests and staff from around the hotel after he starts having way more money than he usually does. Johnny's the only one to believe that Reef isn't the thief (mostly because he feels that Reef isn't smart enough to pull off something like this). After looking through some hotel security footage, Johnny and Reef discover that the thief is apparently just a seagull—later, while trying to catch the bird, Reef questions Johnny on why they can't just tell the others about it, and Johnny explains that they need to get more definitive proof since they all the evidence they have is circumstantial at best. In the end, Reef's proven innocent and it turns out that all the extra money he had was the result of someone in the hotel's accounting department accidentally adding Wipeout's pay to Reef's—Bummer (Reef, Johnny and Wipeout's boss) rectifies this by making Reef wear the Wipeout-costume for a week without pay to make up for all the money Reef got by mistake.