Michael: You never tell me anything, so how the hell should I know what might be important?
This is when someone knows a fact that would be of great importance to the heroes but never says anything, for the simple reason that that person has no idea the fact is important. A subtrope of Poor Communication Kills, and definitely overlaps with Locked Out of the Loop.
Compare and contrast You Didn't Ask, which is where the person who knows the clue also knows its importance, but simply wasn't asked to divulge.
- In Say It Thrice, Danny, Sam, and Tucker never think to mention to the new girl about the rumors concerning the Ghost With the Most and his missing "Mortal Bride." Likewise, Lydia never thinks to mention she was almost married to a ghost once. Without these minor details, no one can make the connection and realize they are dealing with the same entity. Of course, it makes sense that the topics wouldn't come up when talking to near-strangers.
- Rosario Vampire: Brightest Darkness:
- In Act III, Rason confesses that the Holy Lock was never actually made with the express intent to keep a ghoul in check, let alone one as powerful as Tsukune's, but he doesn't actually make this known to the group until after Tsukune has broken six links on the lock. To be fair, the other angels had repeatedly ensured him that the lock was indestructible either way, but still...
- In Act IV, Apoch and Astreal were well aware that Apoch's Laser Blade could penetrate Jovian and Jacqueline's force fields, but don't think to mention it to the rest of the gang until the very minute they've split up to save Moka from Hokuto as well as take on Jovian and Jacqueline, and Apoch isn't with either group that's actually fighting Jovian and Jacqueline. While Apoch has the excuse of having been explicitly told by Dark not to say another word about Jovian and Jacqueline's attack, and obediently doing so because she's Dark's Yes-Man, Astreal just offhandedly mentions it while the others are bemoaning the fact that nothing they do can break said force fields, and is genuinely surprised that they thought as such.
- Radiant Garden Renegades: From the minute Xehanort arrives on Radiant Garden in chapter 4, Kaname, able to sense his darkness and noticing that Kairi is terrified of him, along with Xehanort's Stalker with a Crush behavior toward Rimi, is naturally suspicious of him, but as he doesn't know what to make of it, he doesn't say a word about it to Ansem the Wise until after Ansem reveals that Xehanort has been conducting experiments with Heartless behind his back and writing reports under Ansem's name; he admits that he most likely should have said something before then, but by that point, it's too late.
- In Grave Mentor, the Ancient Ones own this trope, refraining from telling Michel anything that might be useful when he's on earth trying to help Seira combat the magical catastrophes that are happening. It actually manages to get bad enough towards the end of the story that Michel even asks why no one bothered to tell him a few things.
- In Gotham Banksy, the apparition of Batman-hate graffiti garners mere amusement from Oracle and Batgirl, while the police doesn't even bother with pursuing the vandal — because when you live in Gotham capital of murdering crazies, a bit of spray-painting on the wall is positively a charming note. Which let Jason Todd fly under the radar for quite a moment until the Batclan realizes there's more to the paintings than expected.
- In Legally Blonde, the defense team in the Brooke Windham case is so focused on Chutney Windham's actions immediately before the events of her father's murder that they don't bother to ask what she was doing earlier on the fatal day. When Elle finally brings it up during a cross-examination, Chutney casually mentions that she had gotten a perm that morning—which invalidates her alibi of being in the shower at the time of the murder, and eventually leads her to confess to the crime on the stand.
- In The Princess Bride, Inigo Montoya can be forgiven for not realizing that a wheelbarrow might turn out to be of significance:
Westley: What are our liabilities?
Inigo: There is but one working castle gate, and . . . and it is guarded by 60 men.
Westley: And our assets?
Inigo: Your brains, Fezzik's strength, my steel.
Westley: I mean, if we only had a wheelbarrow, that would be something.
Inigo: Where did we put that wheelbarrow the albino had?
Fezzik: Over the albino, I think.
Westley: Well, why didn't you list that among our assets in the first place?
- A variation in Star Trek Into Darkness:
Spock: The admiral's daughter did express interest in the torpedoes, and she is a weapons specialist.
Kirk: What admiral's daughter?
Spock: Carol Marcus, your new science officer, concealed her identity to board the ship.
Kirk: When were you going to tell me that?
Spock: When it became relevant, as it just did.
- In the Dante Valentine series, Danny is forever begging Japhrimel to tell her things. He doesn't until it comes up in battle. When Danny asks why he didn't tell her sooner, he shrugs it off answering, "I did not want to trouble you with something so trivial." He abuses this excuse to the point Dante is often ready to scream.
- Discworld: Samuel Vimes has a moment or two of this in every book he stars in, but Feet of Clay and Thud! probably have the most.
- Inverted in Harry Potter and the Order of the Phoenix. Sirius considered the fact that he and Harry are close to be trivial—or, perhaps, didn't have the patience to deal with his irritating House Elf Kreacher knowing the information. When he yells "GET OUT!" to Kreacher at one point, the House Elf obeys him—by "getting out" of the house and going to Bellatrix Lestrange with news about Sirius and Harry's bond. Bellatrix in turn tells Voldemort, who uses the relationship to set up a dangerous trap.
- The crucial clue that Hercule Poirot needs to solve the mystery is usually something like this. It's lampshaded in The ABC Murders, when he summons the families of all of the victims precisely for the purpose of talking about the trivial things surrounding the murders, in hopes that there will be some small detail that connects all of them. There is, but it turns out to be a Red Herring.
- This was true of Miss Marple mysteries as well, though Christie would usually lampshade and justify the trope. For example, in The Mirror Crack'd from Side to Side, the vital information turned out to be the initial victim's having German measles when she met the killer on a previous occasion. Nearly everyone who relayed the story either didn't bother paying attention to the exact diagnosis or, in the killer's husband's case, lied to cover it up. It isn't until Miss Marple herself gets a full, accurate report that she's able to piece together the puzzle.
- In another Miss Marple short story, the killer turns out to be a woman disguised as a chambermaid; the person deliberately invoked this trope because she knew that people wouldn't bother to bring up a chambermaid entering a hotel room, as it seems so unimportant.
- The Columbo episode called "Lady In Waiting" has a wealthy woman kill her brother and make it look like she accidentally mistook him for a burglar after he tripped the alarm system. Her fiancé came to the house unexpectedly as her setup was unfolding. Only later did he realize (with Columbo's help) that he heard the three fatal shots first, then heard the alarm sound.
- Doctor Who: "The Sontaran Stratagem" has a villainous example: Luke Rattigan gets a phone call from UNIT telling him that the Doctor is coming to see him. Luke, having never heard of him, assumes that "doctor" is only his title. So, when General Staal asks him who the Doctor is, during a confrontation, Luke responds with "He didn't give his name", thus preventing Staal from realizing exactly who he just met until after the Doctor and UNIT private Ross have fled the scene, and they're trying to track them down.
Luke: That doctor, he was in a UNIT jeep.
Staal: ...You said you didn't know his name.
Luke: I don't, he just said "doctor".
- In the season one episode of Farscape, "I, E.T.", the crew is desperately searching for an anesthesia to use on Moya located somewhere on an alien planet, only to find out, at the eleventh hour, from a befriended local that it's a common spice they used in their food.
- In the Gilligan's Island episode "V is for Vitamins", the Professor is concerned about the lack of vitamin C in the castaways' diets and they try to grow oranges, even though the island has the wrong climate. It turns out that the island is ripe with grapefruit and lemons, which Gilligan knew about but didn't say anything because he didn't know that those fruit had vitamin C in them.
- It seems like in House every other episode or so features this — the key turns out to be something that the patient would have gladly divulged (especially as an alternative to the humiliating but irrelevant parts of his life that they unearth while looking for the clue), but couldn't see that it would possibly be relevant.
- In one episode, a man who'd been suffering for years was so desperate for a diagnosis that he took the clinic hostage at gunpoint to force House to diagnose him. In the end, the key to his diagnosis was mentioning that he'd once been to Florida. He'd repeatedly claimed that he'd never been to the tropics, not realizing that Florida counted.
- In an episode of Law & Order: Special Victims Unit, Elliot is accused of murdering a suspect in custody when the man's spleen is found lacerated in an autopsy. When ME Warner, who performed the autopsy, goes to him to apologize for having to implicate him in the man's death, Elliot is horrified at his own actions and says he never meant for anyone to die; he tried to save the man. How? By performing CPR. Which Warner immediately realizes could have caused the injury, meaning his cause of death was something else. She didn't know he'd done it, and none of the people who had witnessed it realized it was relevant at all, let alone the difference between Elliot going free or being charged with murder.
- This trope is pulled in spades in the Ace Attorney series, infuriating the player character to no end. Witnesses will sometimes not bother to tell the player a vital piece of information or give some important evidence that could help clear their name or solve the case because they feel the item/information has no bearings on the current situation.
- A particularly notable example is when Miles Edgeworth completely loses his composure in the middle of court over a playing card that Adrian Andrews has been absentmindedly toying with. She is genuinely confused when he demands to know where she got it and why she didn't tell anyone about it. Turns out it's the calling card of an infamous assassin, which dramatically changes the case.
- Persona 4: Yukiko's knowledge that Adachi was at the inn spending a lot of time with Ms. Yamano just before she died is the first non-circumstantial piece of evidence the group has towards finding out his identity as the true Killer, but she doesn't make this known unless the player casts suspicion on Adachi in the first place... at the very end of the game. To be fair, however, none of them had actually thought to suspect Adachi of being the killer before that point.
- In the Tales Series:
- Tales of the Abyss:
- Jade deduced almost immediately that the "Luke" he was traveling with was actually a replica of the real Luke. Jade didn't tell because doing so would have resulted in massive amounts of existential angst on replica!Luke's part with no apparent beneficial trade-off. In hindsight, that wasn't the best decision. Revealing the truth would have stopped the Big Bad's manipulations, even if Jade wasn't aware of them.
- Luke does this later on in the last third of the game when he neglects to tell the rest of the party the local Deity had contacted him, warning him that the Big Bad had captured it. This one can be chalked up to simple ignorance, as Luke had no idea what the message meant.
- In Tales of Vesperia, Judith knew the truth about the blastia and how they were affecting the planet. Did she share any of this information? No. And when Rita and the others asks, "why didn't you say anything?" Judith's response (as seen during one of the private scenes between her and Rita) amounts to, "it didn't seem important at the time."
- Tales of the Abyss:
- In Galaxion Patty gets bitten by an alien bug. The team worries a bit, but soon lets it go in favour of more pressing concerns, but the fever she develops after a while is actually plot-important. (And how!)
- Antimony Carver, from Gunnerkrigg Court. At the point of Chapter 33, she had enough information about Jeanne, one of the Court's founders, whose information was deliberately hidden or destroyed. This is even lampshaded at some point in Chapter 23 by Jones:
"A lot of information about the origin of the Court has been lost or, in my opinion, deliberately hidden. If you have somehow come across information from that time, it could provide valuable insight. (...) However, such information is useless until properly investigated. When you feel you have uncovered the whole story, please, tell me about it."
- In S.S.D.D, Michael is the only member of a group trying to prevent The Oracle from gaining control who is not from the Bad Future in which it has done so. He is also the only one knows that British Intelligence created something called the Echelon Plug-in (he was given a copy of it). Two problems. First, he's the group's Butt-Monkey, so nobody else tells him anything, which means he has no idea what the Oracle is, never mind that it exists (he actually has to be told that the "Old Man" and The Oracle are the same thing. Second, he's the group's Butt-Monkey, so nobody listens to him, which means the others have no idea what The Echelon Plug-in is, never mind that it exists. When they finally tell Michael about Oracle, Michael makes an offhanded comparison of the two programs and the others realize that the Oracle and Echelon Plug-in are one and the same. In other words, the Oracle already exists in Michael's time, which explains a lot. The page quote comes from this.
- Something of a mutual example in the finale of Avatar: The Last Airbender: After Zuko attacks Aang for taking a break from training and they each explain their sides, it turns out both had a key piece of information the other lacked. The Gaang had decided to push back their timeline (waiting until after Sozin's comet had passed to depose the Fire Lord) because they didn't think that a one-day power-up would do much to change the status quo of the hundred year long war they were looking to end. Zuko didn't tell them that the Fire Lord planned to use the power-up to commit genocide on the Earth Kingdom because he didn't think they needed the added motivation to do what (he thought) they were already planning on doing anyway. Had either side spoken up earlier, they all would have been more prepared for the final battle.