A lot of times in life, lots of people jump to conclusions about certain kinds of things. After a little bit of misunderstanding, once a character finds out what's really going on, he will then proclaim rather blatantly that he knew it all along. This is something that a Large Ham, a Small Name, Big Ego, an Idiot Hero, a Know-Nothing Know-It-All, or a Miles Gloriosus is expected to do.
- After the first stage of the Chuunin exams in Naruto, Proctor Ibiki explains that there are two members of the test takers who served as cheating fodder for the others, which several shinobi noticed, but Naruto is not among them. However, once Ibiki explains this, Naruto acts as if he figured it out halfway through.
- In Pretty Cure All Stars DX 3, Cure Marine and Cure Rhythm start panicking when Cure White, Cure Egret, Cure Mint, Cure Aqua, and Cure Berry start taunting Freezer and Frozen. When it turns out that their taunting leads the two to freeze the water they were trapped around, Marine instantly declares that it was a great plan and she knew it all along. The others don't buy it.
- In the Donald Duck comic "The Old Castle's Secret", after the "ghost" is revealed to be a guy using invisibility spray, Donald tries to claim he knew it all along (rather than being terrified out of his wits while Huey, Dewey and Louie single-handedly solved the mystery themselves). His nephews are not amused.
- Played for laughs in this video where someone plays Kirby Super Star and is terrified of Waddle Dee. A bystanding Straight Man makes some rational observations on him, all dismissed by the player as "Lies!" The friend eventually tells the player how to get Kirby to properly attack (to which the player expresses amazement), and once Waddle Dee finally dies, the player exclaims, "It worked! I'm a genius!"
- A Goofy Movie: At the Neptune Inn, Pete pranks the Goofs by bursting into their room with a policeman act, and Goofy claims to have known it was him.
Goofy: You sure had him fooled, Pete.Max: Me? You jumped out of your skin!
- The Land Before Time: After Cera was cornered by a pack of Pachycephalosauruses that were scared off by a seemingly monstrous tar blob monster, she becomes afraid that the monster will get her too. However, the monster turns out to be Littlefoot and the others all covered with tar. Once Cera realizes this, she then proclaims that she knew all along that it was them, being the ego brat she is.
- In The Little Mermaid (1989), this was Scuttle's response after Sebastian tells him that Ariel had gotten legs (Scuttle knew that something was different about Ariel, but kept guessing right off the bat that it was something else).
- Harry Potter:
- In Harry Potter and the Chamber of Secrets, Professor Lockhart claims, after Professor Snape hits him with a disarming spell during a demonstration, to have known what Snape was going to do, and that if he wanted to block it he could have.
- When Harry and Ron are hiding in the teachers' room and someone suggests a remedy for the students' petrification, Lockhart is heard to mumble something along the lines of "Of course, it's what I've been saying all along."
- In Pete's Dragon (1977), in the song "Passamaquody," Dr. Terminus repeatedly mispronounces the town's name, and when the angry crowd corrects him, he responds "That's what I meant to say," and "I know."
- In Stage Door, Anthony Powell is a nervous wreck on opening night because Terry Randall, the actress he picked for the lead part of the show he's producing, has been terrible during rehearsals, and the only reason he cast her in the first place was because his mysterious benefactor insisted he cast her. When she ends up giving a brilliant performance opening night - due to circumstances he's entirely unaware of - Powell acts not only as if he knew Terry was going to be good all along, he also acts as if he always knew the benefactor was in fact Terry's father (who, ironically enough, was hoping she'd fail so she'd quit acting).
- C-3PO says the line verbatim in The Empire Strikes Back, claiming he knew all along that Lando Calrissian was really on their side. Of course, this seems more like wishful thinking that just happened to be correct, since 3PO was already having a pretty bad day what with being dismembered and carried around on Chewie's back like a bookbag, and he really wanted to catch some kind of break.
- Lynch, Bud Fox's boss in Wall Street, tells him "The minute I laid eyes on you I knew you had what it took," when Bud's star is rising. When Bud is arrested, Lynch has his own personal retcon, saying, "The minute I laid eyes on you I knew you were no good."
- Amelia Peabody and her husband Emerson both like to claim to be better at detective work than they actually are:
- In The Curse of the Pharaohs, most of the "deductions" Emerson claims to have made were actually things he had no idea about until the killer confessed.
- In The Deeds of the Disturber, Amelia gives The Summation to their assembled friends, explaining why one person and one person only could be the mastermind behind the murders. When she and Emerson are in bed together later, however, they both confess that they had both suspected the wrong person right up until The Reveal.
- In Cards on the Table, when Hercule Poirot reveals the identity of the murderer, Ariadne Oliver - who by this point has accused just about everyone - declares that she'd always said they'd done it.
- In the Sesame Street book, The Monster at the End of This Book, Grover is trying to stop the reader from reaching the end of the book because he doesn't want to get to the monster, and tries various methods to prevent it from happening, none of which works. In the end, he turns out to be the monster in question. He tries to play it off, admonishing the reader for being scared, then walks away feeling embarrassed.
- Buffy the Vampire Slayer: Willow, on learning of Xander and Cordy's makeouts.
Willow: I knew it! Well, not in the sense that I actually knew anything, but you two were arguing way too much!
- Community's foray into parodying G.I. Joe: A Real American Hero, "G.I. Jeff", sees Zartan mutter "Called it" at Destro's farce of a funeral when Cobra Commander admits to loving the late arms dealer.
- Doctor Who: Most certainly NOT Played for Laughs in "Midnight". After claiming loudly and vocally that the Doctor was possessed by the entity and that he should be thrown out of the airlock, the mother weakly claims that she knew that it wasn't him all along. She wisely shuts up after the Doctor gives her a Death Glare.
- Played with in The Flash (2014), when Barry Allen told Joe West and his daughter Iris about his ordeal on Earth 2. At one point he revealed that Iris on Earth 2 was a police officer.
Iris West: Told you I would have made a great cop!
Joe West: Don't get any ideas.
- In Under the Umbrella Tree, Jacob's catchphrase is "I knew that" whenever he gets a fact wrong and someone else corrects him.
- In Rosencrantz and Guildenstern Are Dead, Rosencrantz thinks he hears music, but decides he must be imagining it. Guildenstern then tells an allegorical story about a man who sees a unicorn but doesn't believe it until other people also say they can see it (and the more people see it, the less fantastic they find it). By the time he's finished the story, Rosencrantz has decided "I knew all along it was a band." Guildenstern sarcastically echoes "He knew all along it was a band."
- In Far Cry 3, Player Character Jason Brody must go undercover as Foster, one of Hoyt Volker's privateers. This includes torturing his own brother Riley to maintain his cover. Then in the evening, Jason and his ally Sam go to play poker with Hoyt, planning an Assassination Attempt on Mr. Volker. Instead, Hoyt stabs Sam to death at the table and smugly tells Jason that he already worked out who Jason was a lot earlier, which means Jason's attempt at infiltrating his men was All for Nothing except to satisfy Hoyt's sadism.
- Star Wars:
- After the player character learns from Darth Malak that he is actually Revan, Jolee Bindo tells him that he had known that the individual was Revan the entire time but felt it was not his place to tell Revan that. He goes on to tell Revan that it was still better that he knew the truth.
- In Star Wars: The Old Republic, at the end of the Bounty Hunter's Story Quest on Balmora, the Hunter can claim that they knew all along that their employer's slave was actually a rival hunter in disguise. Their companion Mako doesn't sound too convinced.
- In Doki Doki Literature Club!, if you don't write your first poem in Yuri's style, she can tell your character hasn't written poetry before, and explain why she knows it. If you do write it to please her, she'll first assume it's not your first poem, but upon being told it is, will backtrack, take a second look, and give the same explanation for why she supposedly knew all along.
- In the good ending of Shinrai: Broken Beyond Despair, after Raiko manages to prove that the falsely accused Kamen did not commit the murders, most of Raiko's fellow survivors apologize to Kamen for doubting their friend. The only exception is Mika, who, despite having jumped on the bandwagon and having accused Kamen, claims that she knew all along that Kamen was innocent and wanted to test whether Raiko could prove it. Other characters chalk this up to Mika being bad at apologizing.
- Woofer on Clue Club always brags to Wimper of how he knew who the mystery's culprit was and his modus operandi.
- Parodied in Freakazoid!. Freakazoid is forced to ignore his arch-nemesis, the Lobe, as he wreaks havoc all over the city, as part of the Lobe's request on Freakazoid's birthday (long story). Eventually, Freakazoid reads one very important detail and shouts, "I KNEW IT!" But a caption appears on the screen saying "NO, HE DIDN'T."
- Gravity Falls: After Dipper admits to his crush on Wendy due to a rather stressful situation occurring during an adventure, Wendy, flattered, admits that she knew, having heard Dipper mutter his thoughts under his breath multiple times for half the summer.
- Lilo & Stitch: The Series: Pleakley tends to do this after he's been corrected about something Earth-related since he's a self-declared "expert" on Earth. For example, in "Splodyhead", he is led by Lilo to believe that the reason Niʻihau, which they and the other main aliens travel to in the episode, is called the "Forbidden Island" because the island has some "ancient evil mojo tiki curse", and he becomes utterly convinced about this after they get stranded on the island thanks to the episode's title experiment. After Nani and David rescue them hours later, the latter tells Pleakley that the real reason for the island's nickname is because it's forbidden from outsiders without an invitation. After expressing shock that there was no curse, Pleakley quickly "corrects" himself to say that he knew that.
- Littlest Pet Shop (2012): In the series finale, after Blythe reveals to her father Roger that she can speak to animals, he casually responds that he always knew. Later on, when she states that he must have some concerns about her powers, he once again casually dismisses it. It turns out that he was fully aware that his late wife had the same ability ("there's no secrets in marriage") and that Blythe had inherited it.
- My Adventures with Superman: In the fifth episode, "My Adventures With Mad Science", it's revealed that Jimmy has known Clark was an alien for years. He just didn't feel it was his place to reveal his knowledge, waiting for Clark to tell him on his own terms.
- In the Scooby-Doo, Where Are You! episode "Never Ape an Ape Man", Shaggy gets "grabbed" by a stuffed ape. Upon being told this, he says, "Well, I certainly hope you don't think he had me fooled for a minute. I knew it all the time." Scooby sees right through him.