An organization, often a Government Agency of Fiction, deliberately releases secret information, sometimes within a work of fiction, in order to invoke a Cassandra Truth. Alternatively, an individual or small group may do this to get the word out to allies and others in the know despite people/groups/governments who don't want the word to get out; the fictional/tabloid nature of the outlet provides cover for these Cassandras to stave off retaliation from their opponents. They're just smart enough to know that You Wouldn't Believe Me If I Told You. It also allows them to honestly state, "Well a lot of people got that idea from this book, which is a work of fiction". They can then turn on their critics and say they're too credulous or are confusing fiction and reality.
The differences between this and Sarcastic Confession are that the confessors aren't being sarcastic, and they are addressing themselves to many people rather than one or two. Unlike a Public Secret Message, which is published in the open but in code, a Cassandra Gambit is straightforward: what is said is what is meant. She knows others won't believe it, but hopes someone out there ("the right listener") will believe and act on it.
Super trope of Fiction as Cover-Up. Compare Getting Crap Past the Radar, Hidden in Plain Sight, Refuge in Audacity and Sarcastic Confession. The topic these Cassandras are warning about is likely to be the Elephant in the Living Room. Strategy #1 of The Thirty-Six Stratagems.
- In Amagi Brilliant Park, the cast of the park are in fact magical beings from the parallel world of Maple Land, and really do have magical powers; the mascots are real creatures, not people in costumes, and the dragon is not animatronic. The children of course believe it, just as they'd believe the Mickey Mouse at Disneyland is the real deal, but the adults don't. When Kanie is introduced to the park, he thinks the staff are all just really dedicated to keeping up the act and it takes a Magic Kiss from Latifa that imbues him with mind-reading powers before he believes any of it.
- Fails spectacularly in Les Tuniques Bleues: General Alexander holds a meeting to explain the battle plan. He has Chesterfield and Blutch stay behind to make sure they've memorized it, and arranges for them to be caught in enemy territory. It backfires when the Confederates interrogate Blutch first, who glibly tells them every last detail about the plan, which makes them suspicious. Then they interrogate Chesterfield, who, being much more... patriotic, refuses to answer even after days of torture that even the Confederate soldiers are worried about. Finally Chesterfield appears to crack and gives them the battle plan... that he made up. Which, of course, turns out to be Alexander's real plan.
- More than one Harry Potter fic uses this trope to help hide the magical world. Sometimes the characters even write and release Harry's life story to do it!
- BURN THE WITCH (Miraculous Ladybug): Gabriel exploits this by deciding not to do anything about Lila aside from canceling her contract and filing a restraining order. As he explains to Nathalie, even if Lila suspects his Secret Identity as Hawkmoth, she's now widely known to be a manipulative liar. So long as Hawkmoth doesn't do anything to retaliate against her, any claims she makes about his identity will go ignored, dismissed as her frantically lashing out against anyone she perceives to have 'wronged her'.
- Deep Cover: Russell has to Take a Third Option when asked by a gang of thugs if he's an undercover cop. If he lies, then any future arrest would be worthless because it'd be considered "entrapment". And of course, if he tells the truth, they'll kill him. So he just tells them the truth in a way that makes it seems ridiculous. (Note: This is actually a case of Artistic License Law. Real cops don't have to tell their marks that they're undercover. The entrapment clause doesn't work that way. Because if it did, there'd be a lot fewer arrests and a lot more dead cops.)
- Men in Black: Played for Laughs. You know all those tabloid stories that are obviously just made up? Yeah...
- Star Wars: Used by Count Dooku in Attack of the Clones, when he told Obi-Wan Kenobi that much of the Galactic Senate was under the control of the Sith. Obi-Wan and the other Jedi interpreted it as a lie intended to divide the forces of the Republic and make them suspicious of each other. Unfortunately for them, Dooku wasn't lying.
- The alchemist gives this advice to the protagonist in The Alchemist, a book by Paul Coelho.
- Actually done by the original Cassandra in the book Goddess of Yesterday. In the climax, the heroine has regained the infant prince from the Trojans, and has to walk out of the city. During the unbearably tense walk (where she has to act totally natural when all her instincts are screaming to get the hell out of there right now) she hears Cassandra screaming from the battlements that a servant girl has kidnapped the prince and will return him to the Greeks. She panics...then realizes Cassandra's plan is working perfectly and no one is paying attention to her, and the baby prince is safe not long later.
- In play for a time in the Harry Potter universe, when The Quibbler (regarded as an unreliable tabloid) is used to get the word out about Voldemort when The Daily Prophet adheres to the Ministry of Magic's official line (that Voldemort is long gone/dead).
- Star Wars Legends: In Darth Bane, Bane allows a few drunkards to see him, while acting obviously unrealistic. He knows that when they tell their seemingly false story it will not be believed and work to discredit more believable sightings.
- The Equalizer. The psychiatric version also happens in "The Last Campaign". McCall has to get inside a mental hospital where his client is being held incommunicado, so he tells the doctor that he used to work for an international organization of spies, and he wears black so he can fade into the dark during night operations. Later he needs to talk to another patient, so he truthfully explains to the doctor that she's also an ex-spy who's one of his agents.
- Subverted in Lucifer (2016) when the title character also has to Go Among Mad People. He assumes that anyone strolling into a mental hospital and claiming to be the Devil will have no problem being admitted, but it turns out the hospital is at full capacity, so only those who are a danger to themselves or others can be admitted. Lucifer has to slam the orderly against the reception window to convince him that he at least fits the latter category.
- Used in the Mission: Impossible episode "The Diplomat", when enemy spies have found the locations of four key US defense stations. Jim Phelps lets himself get discovered as an undercover US agent, so the enemy will distrust their discovery when he confirms it is accurate.
- Person of Interest. Finch attempts to get out of jury duty by explaining that he doesn't trust the government because an evil supercomputer is trying to take over the world. In another episode, in order to get himself admitted to a psychiatric ward, he earnestly tells the doctor about all the people who are trying to kill him.
- Seven Days: a Conspiracy Theorist gets Frank to go on TV, and Frank tells the world about the Project. Nobody believes him. It helps that he starts off by telling them that he was "recruited" from a mental institution, also true. Suddenly, no one wants to listen to him.
- In Stargate SG-1, Wormhole X-Treme!, a Show Within a Show that parodies the main show, is allowed and even encouraged by Stargate Command, because, well, this.
- During one episode of Supernatural, protagonists Sam and Dean Winchester get themselves admitted to a mental hospital by telling the staff that they are monster hunters looking to stop the apocalypse that they accidentally started. Unfortunately this backfires because the one person who would actually believe them is the Monster of the Week, so it only tips them off that a couple of Hunters are on their trail.
- Battlestar Galactica (2003). While Gaeta is secretly coordinating The Coup from Mission Control, he tells Admiral Adama that all the mysterious problems they're experiencing may be the result of sabotage.
- Many games set in "the real world with a masquerade in effect" imply the game itself is this.
- In Arcanum: Of Steamworks & Magick Obscura, the people behind the half-ogre breeding conspiracy routinely allow manic crackpots to find out about pieces of the conspiracy (and later kill them off to provide more fuel for the other crackpots) in order to convince the public to dismiss it as just an absurd idea.
- El Goonish Shive: Justin wrongly believes this to be Arthur's intent when he publicly acknowledges the authenticity of footage of a superheroine fighting a fire golem, then making cryptic predictions about future magic users and putting on a wizard costume before leaving. Mr. Verres immediately jumps down Justin's throat, saying this technique always backfires and Arthur would know that; sure enough, the next day a radio poll has only 20% of respondents doubting the truth of the incident, with extras comparing skeptics to moon landing conspiracy theorists.
- As he points out...it only works when you have an alternate plan to handle LATER things that corroborate the story. Making the truth sound ridiculous doesn't work if evidence keeps piling up. (In this case, a person is seen using magic on the news, specifically Pandora.)
- Also, Arthur's too somber to give the impression he's mocking the idea, too lucid (and terse) to give the impression of senility, and has a well established reputation as a hard-line skeptic with absolutely no ties to anybody who might want to cover up evidence of magic. And as the latter is very untrue, many subordinates who pulling off this gambit could be reliably delegated to. What Arthur's plan is remains unclear, but it appears he's preparing to sacrifice at least that part of the Masquerade.
- With the revelation that Magic has a will and does change how it works in response to too many people knowing about it, Arthur's plan is getting enough people to believe in the reality of magic so that magic changes the way it works so that people who can use it now won't be able to and it will be several decades before enough is learned about the new way magic works for some people to figure out how to use it again, thus eliminating for some time the problem of having to cover up the existence of magic because there won't be any around to cover up.
- Arthur's Batman Gambit fails because of a crucial piece of information he was unaware of.
- Scandal Sheet: The Comet exists for this.
- In the Halo ARG HUNT the TRUTH, Benjamin Giraud comes close to breaking the truth on the SPARTAN-II program, but ONI's able to counter it by deliberately leaking truthful information to Ben, but incorporating an easily detectable flaw in the actual files so that, in combination with Manipulatively Editing their previous footage of him and forcing his sources to recant, he'll be discredited in the public eye.
- SCP Foundation:
- A common WMG and Running Gag, both here and on its own website, is that the Foundation itself is this.
- Several articles involve containment procedures that include deliberately letting the public know some of the truth, but framing it in a deliberately absurd fashion. The most notable of the bunch is SCP-1000—the article goes so far as to include an addendum by the head researcher explaining that, yes, it's that Bigfoot, Bigfoot is real, and the fact that it sounds so silly is a sign that their cover stories are working.
- On Futurama, when Area 51 recovers a crashed "spaceship" (Bender) and alien "invader" (Zoidberg) in 1949, they invite a conspiracy theorist to tour the facility specifically because no one will believe him and he doesn't know how to operate his own camera.
- Area 51 in Kim Possible plays this trope to a T, so much so that Kim and Ron are surprised to find out that Area 51 is exactly what the tabloids claim it to be. The gambit still failed where it mattered most: Dr. Drakken believed the stories, and decided to invade Area 51 to get his hands on the alien technology.
- In an episode of Kung Fu Panda: Legends of Awesomeness, Po disguised as a criminal to trick Tong Fo into telling him the location of the Sacred War Hammer of Lei Lang. The only problem was, Tong Fo initially dismisses Po and becomes shady that the criminal he's disguised as is even in prison to begin with. Po then tells Tong Fo to his face that he's the Dragon Warrior in disguise, and the Furious Five will be after him. This gets a laugh from Tong Fo and dismisses this truth as utter ridiculousness. Later he finds out that Po was telling the truth and lampshades this:
Tong Fo: You're a trickster, Dragon Warrior. You told me the truth as if it was a lie. But, it was the truth, which made me think: how? And I'd say: it's 'cause you're...
Po: What? Cunning? Subtle? Finessey?
Tong Fo: (sarcastically) ... Yeah, all those things.
- South Park: Inverted in The Mystery of the Urinal Deuce, they discuss 9/11 conspiracy theories. George W. Bush himself tells the boys that the government caused 9/11. Later however it is revealed the government is responsible...for the 9/11 conspiracy theory movement. They create the theories so the U.S. government appears all-powerful, at least to the stupidest 25% of Americans who blindly believe conspiracy theories.