When a hero delivers a Cassandra Truth, they usually have trouble convincing anyone to believe them. Sometimes they get lucky though; maybe they're speaking to a Reasonable Authority Figure who hears them out and decides to investigate further or perhaps irrefutable proof of Demonic Alien Ghosts just burst through the wall. Either way, somebody you expect to have more influence than you is convinced that you're right...but they're no more able to convince anybody else than you.
Maybe the Police Are Useless for everyone, perhaps the person you've convinced can't convince their bosses, or it might just be that your new confidant already has a reputation for believing crazy things. Par for the course if an Extra-Strength Masquerade is involved. Bonus points if a scene where they try to convince someone to believe them parallels one they had with the heroes. Either way, they've put their name on the line but ended up co-signing your discredit card.
- Monster: Over the course of the series, various people grow convinced that Dr. Tenma is telling the truth about Johan committing the murders that he is accused of and/or are persuaded to work toward exonerating him upon realizing that he is a good person and does not deserve to be a fugitive, up to and including Inspector Lunge. However, they still remain largely powerless to prevent the authorities from attempting to apprehend Tenma, save for trying to take matters into their own hands.
- In Chicken Little, when the title character finally succeeded in convincing his friends that "the sky is falling" (in other words, an alien ship was visiting), when they tried to back him up the rest of the town didn't believe them either.
- Recess: School's Out: TJ witnesses suspicious activity at the school and reports to the cops only for them to laugh him off. TJ then rallies his friends from their camps and desperately tries to convince his friends that is happening at school, but they think he made the thing up to force them out of camp, until they all witness a giant satelite dish emerge fro the school roof. Later when TJ gets captured, TJ's friends report the incident to the cops only for them to laugh at the gang too. Even when Miss Finster comes by with the same story, the cops laugh her off too.
- Doug's First Movie: Doug and Skeeter tell the Mayor about the swamp creature they found, but she can't publicly declare its existence without backlash. They try, but an attempt to capture the beast by a Corrupt Corporate Executive impedes this.
- In Breakin', the main character manages to get her extremely sceptical agent to come down and watch a street dancing contest. This convinces him that they have potential and he agrees to take on her friends as clients too. Unfortunately he has even more trouble convincing his contacts to take them seriously.
- In the middle of The Terminator, Sarah Connor seems happy to accept the psychologist's explanation that Kyle Reese is a paranoid schizophrenic, and the Killer Robot is just on PCP. By the beginning of the second film, she's locked up in a mental asylum for insisting that Reese's story about the impending apocalypse is true.
- 12 Monkeys has an interesting variation of this trope. Dr. Railly doesn't believe James Cole's claims that he's from the future, but when he disappears, she investigates his claims and finds corroborating evidence. When Cole returns, Dr. Railly has difficulty convincing Cole of the truth, as he has accepted her explanation that he is delusional. Ultimately, they are both on the same page, but can convince no one else as they race to save the future from The End of the World as We Know It, while being chased as hunted fugitives and suspected terrorists. But none of that matters, as it turns out that You Cannot Change The Future and the film ends on the virtual definition of a Downer Ending.
- In the Child's Play series, Mrs. Barclay ends up being committed because the cops who witnessed Chucky refused to back up her story.
- In Happy Accidents, Ruby starts wondering whether Sam is telling the truth.
- In Edge of Tomorrow, after William Cage dies several times after fighting the Mimics in a doomed frontal assault, he tries to warn his squad-mates that the counter attack was going to fail, and the Mimics would take over Earth, but they tape his mouth shut shortly before they go off to battle and die. He then joins Rita Vrataski, who had gone through the same thing some time earlier and who has secretly partnered up with the foremost expert on the Mimics. When Cage asks her that if they know about the Mimics ability to manipulate time to their advantage, why they don't take that information to the high command so they can formulate a battle plan, Rita answers that she tried numerous times, and for her trouble she was either put in a psychiatric hospital, or was dissected to see if anything could be learned from her physiology. As for the researcher, he says when he tried telling them everything he learned about the Mimics, and that he had invented a device that could track down their leader via their Hive Mind mentality, he was labeled a crackpot, and dismissed.
- Avalanche Sharks features quite a bit of this. Old Duffy is widely dismissed as a crazy old hermit by the local sheriff, ski patrol people and spring-breakers when he shouts out warnings about sharks in the snow. When the sheriff is convinced the sharks are real by his wife, and some of the spring-breakers find evidence of attacks while looking for the brother of one and the cousin of another. None of them are given much credence by the local mayor, ski patrol man and resort owner. The spring-breakers try to warn some of their friends on the mountain right before another attack, with only one girl listening to them and leaving in time, while even the ski patrol guy finally starts believing after seeing an attack, but its difficult getting the lift operator to start sending people down right before the Characters Dropping Like Flies climax.
- Mulder usually had this problem after convincing Scully on The X-Files. Other characters they convinced also tended to suffer this trope (if they weren't blackmailed or bribed by the Ancient Conspiracy).
- In Angel's "Shiny Happy People" Fred catches Cassandra Truth literally from Jasmine's blood, and then figuratively when she talks to the only other person so far to see the truth (who had been converted earlier), who explains to her "she [Jasmine] must die" and "you've been called".
- Motherland: Fort Salem: When Tally realizes that the Spree are disguising innocent civilians in a bomb-equipped Spree truck, she warns Anacostia, who believes her, but is ordered by Alder to kill them all anyway. When Tally tells Abigail and Raelle this later, they also instantly believe her.
- In Mass Effect 3, Cowboy Cop Garrus Vakarian details to Commander Shepard how he successfully convinced his usually skeptical By-the-Book Cop father (that he was a bit estranged with) that the Reapers are real. Since his father has connections in the top echelons of the Turian Hierarchy, he tries to convince the Primarch. The Primarch is... less convinced. Averted once the Reapers finally arrive; Garrus's dire portents are vindicated and he gets catapulted to the top echelons himself and has generals saluting him.
- Jackie Chan Adventures:
- At the end of the first season (after spending the entire series thus far reprimanding Jackie whenever he brings up magic), Captain Black finally witnesses magic firsthand. In the next season, Black tries to report intel about demons to his superiors, and they decide that he's gone crazy.
- Jade loves to share stories about her supernatural adventures to her classmates, but naturally they don't believe her. One of them, a boy named Drew, is especially mean about ridiculing Jade's claims. But when Drew learns that magic is indeed real, Jade decides to turn the tables and humiliate him when he tries talking about it to his class.
- In the Invader Zim episode "Vindicated," Dib thinks he's managed to convince the school's guidance counselor, Mr. Dwicky, that Zim is an alien who's trying to conquer Earth, but Dwicky tells a colleague that he's just playing along so Dib will eventually feel comfortable enough around him to confess what always has him so on edge and antisocial. Dib feels very hurt once he realizes that Dwicky never really believed him, but then Zim shows up without his disguise because he fell for the trap Dib and Dwicky set up, pretending to be fellow aliens offering him superweapons. Then the aliens Dib and Dwicky pretended to be show up too, superweapons in tow, and Dwicky, childhood belief in aliens now reignited, accepts their offer to travel the stars with him, unfortunately bringing with him the video evidence of Zim's alien identity.
- In The Simpsons, Lisa discovers that town founder Jebediah Springfield was secretly a villainous pirate. No one believes her story except Homer, who is smart enough to know Lisa tends to make the right assumptions on these things. They fail to convince anyone else and Homer is stripped of his role in the town parade as punishment. Subverted when Lisa realises that the museum curator covered it up (he relents, but Lisa decides that the lie inspires the town and leaves things be).
- In the TaleSpin episode "It Came from Beneath the Sea Duck", Kit is chewed out by Rebecca for taking Molly outside the apartment while babysitting (in reality this was for a load of convoluted reasons). Baloo is smart enough to suggest letting Kit explain what happened, however Rebecca just assumes that Kit learned his irresponsible behaviour from him and shushes him too.
- Phineas and Ferb has an episode where Candace finally convinces her mom that her brothers have done something bad, then she has trouble convincing Lawrence. When Candace points this out to her, however, Linda fails to realize it.
- In another episode, Stacy and Jenny join Candace in busting Phineas and Ferb, but when they try to tell their mom she merely thinks that Candace is rubbing off on them.