Infallible Babble

"Law of Productive Gullibility (Ruby Rule): Whenever anybody comes up to you with a patently ludicrous claim (such as, "I'm not a cat, I'm really an ancient Red Dragon") there's an at least two-thirds chance they're telling the truth. Therefore, it pays to humor everyone you meet; odds are you'll be glad you did later on."

- The Grand List of Console RPG Clichés, #101.

Information's answer to Chekhov's Gun.

When provided information in video games, you need not ever take it with a grain of salt. In fact, you can be absolutely confident that the information is entirely accurate. This holds true even if the information is based on nothing but a rumor, or said in passing or in uncertain terms.

For example, if someone tells you "I think King Samuel's apprentice maybe keeps an Asagron Mythril in the desk of his workshop", you can be absolutely certain that when you travel to the apprentice's workshop and search inside his desk you will find an Asagron Mythril.

Nor do you ever need to consider the source; the delirious town drunk is just as trustworthy as a respected high-ranking government official (often more so, in fact). The only exception seems to be gossip about your own adventures, and even then they usually get it right.

Commonplace in other media. Indeed, one reason why we are often presented with the true facts before the Malicious Slander is because the audience will often take the slander as true otherwise, relying on this.

Often goes hand-in-hand with the principle of the Inevitable Tournament. This often happens in the same kind of story where All Myths Are True.

Film

 * Played with in 2012, in which absolutely everything the zany Conspiracy Theorist spouts turns out to be down-to-the-minute true... except for.

Literature

 * In Harry Potter and the Half-Blood Prince, Dumbledore openly states that everything from this point on regarding Voldemort is unconfirmed theory and speculation. Despite this, nearly everything Dumbledore says is pretty much dead on. This isn't as farfetched as it sounds as they do have a decent amount of information to base these theories on, (and it's Dumbledore.)
 * Well really, Dumbledore was stretching the truth to breaking point when he said that everything was just speculation, since he later says that he considered his theory confirmed as early as the second book. And as book seven reveals, there are certain elements of his Batman Gambit that he never tells Harry, despite his promise. Though it's not that relevant to the plot, Dumbledore was wrong about the victims used to create the horcruxes: They were not all significant murders. They varied in importance from his biological father to a Muggle Tramp.
 * Harry's own babble is apparently infallible, as all of his ludicrously specific wild guesses about the Hallows turn out to be dead on. For instance,
 * The cursed ring was a stretch, but there isn't much else the snitch could have been for, particularly since it was implied it would "open", and was therefore containing a plot gizmo. Looks like a case of Genre Savvy.
 * In earlier books, the fake "prophecies" that Ron and Harry whip up in Divination class have an ironic tendency to come true, despite having been deliberately concocted because they'd both failed to divine anything.
 * Aversion and Lampshading: Robert Jordan's Wheel of Time books have tons of rumors popping up, most of them false. But the series is stuffed with Poor Communication Kills, so the main characters can be very gullible, which is mocked very well in ISAM's parody summaries.
 * Sort of comes up in Allegiance. Two Imperials have betrayed Mara Jade, and now they're trying to kill her. She recognizes a tactic they're using, in which one sneaks after her while the other gets talkative, distracting her and covering any noise the first makes. But, she thinks, you are not supposed to give out actual useful information while doing this, and in this case it means they're either stupid or very, very confident. The talking one mentions stormtroopers deserting, which happens to be plot-important.
 * In Robert E. Howard's "Shadows in Zamboula", Conan the Barbarian is thoroughly warned about staying with Aram Baksh, where he hired a room.
 * In The Hour of the Dragon, the rumors that Conan is Not Quite Dead spread over the entire kingdom without getting mangled.
 * In "The Phoenix on the Sword", Conan has heard the rumors on Epemitreus's ghost, down to his purpose being to aid Aquilonia; Epemitreus has only to explain that Conan's destiny is tied to the land.
 * In most of H.P. Lovecraft's stories, especially "The Shadow Over Innsmouth", in which, in the titular village, the insane ramblings of the town drunk all seem to be horrifically true.
 * Tyrion in A Dance With Dragons treats his father's last words "wherever whores go" as this, considering them to be a crucial hint as to where his lost love Tysha disappeared to.
 * In most of H.P. Lovecraft's stories, especially "The Shadow Over Innsmouth", in which, in the titular village, the insane ramblings of the town drunk all seem to be horrifically true.
 * Tyrion in A Dance With Dragons treats his father's last words "wherever whores go" as this, considering them to be a crucial hint as to where his lost love Tysha disappeared to.

Live-Action TV

 * An offshoot of this is subverted hard in Angel. Similar to rumors, Prophecies Are Always Right - except
 * Also except for at least one prophecy, which is correct, but horribly mistranslated. In a memorable event at the end of the first season,
 * Also subverted in Firefly, where characters bandy about various theories about the Reavers. Mal suggests they've been separated from civilization too long, and Kaylee suggests they reached the edge of space, saw nothing beyond, and went insane as a result.
 * Played straight with River, whose seemingly random utterances often have a ring of truth to them. It is justified though, as
 * Somewhat related: In far too many episodes of The X-Files, Mulder will randomly spout a random guess about the nature of the Monster of the Week. No matter how little information he has, whether that information is remotely reliable, or how many other explanation there could be for it, his random guesses are always right.
 * Specifically inverted in the episode "War of the Coprophages", which mostly consists of Scully debunking Mulder's various (increasingly insane) theories about why people in a particular town are dying in cockroach-related ways.
 * Inverted in Psych. Shawn regularly tells outlandish lies in an attempt to make himself sound more interesting. And he does this in addition to the gimmick where he claims to be a psychic. An inversion because Shawn knows they're lies and they end up being true in spite of this.
 * One Doctor Who executive producer and writer complained at length in a episode commentary about the fact that anytime a sci-fi character starts giving exposition, the audience automatically believes him, despite the fact that he may be very well be wrong or confused.
 * In Power Rangers RPM, a guard remarks that a Venjix hardware detector has been giving him false positives all day when it goes off on Tenaya 7. In the two-part finale it turns out.
 * In Power Rangers RPM, a guard remarks that a Venjix hardware detector has been giving him false positives all day when it goes off on Tenaya 7. In the two-part finale it turns out.

Tabletop Games

 * The Enemy Within campaign for Warhammer Fantasy Roleplay gave the GM several rumours that the players might encounter while talking to people. Some had a grain of truth, most were just rubbish.
 * One held that the mayor of some town was a Chaos Cultist who was feeding his cat milk mixed with human blood. Several people swear they heard the mayor telling his cat to "drink your bloody milk!".
 * Dungeons & Dragons adventures from early versions on had a list of rumours that can be picked up if someone does information gathering - usually at least a dozen lines each marked as false or true, and even some of the true ones may appear suspicious or important while actually lacking any connection to anything remotely plot-relevant.
 * Famously weaponized in the tale of The Head of Vecna.

Music

 * Panic! at the Disco's "I Write Sins Not Tragedies" implies that the protagonist is going to leave his fiancée at the altar ("technically our marriage is saved") because he heard a waiter call her a whore.

Video Games

 * Nearly every Role-Playing Game in existence.
 * Any game in which an NPC promises to let you past somewhere if you pay them a certain amount of the in-game currency, especially obvious if they are enemies and would normally be sure to exploit you.
 * Inverted in Final Fantasy VI, where the people of Zozo lie. Always lie, mind you. Nobody ever tells a normal rumor. This culminates with one person saying "Zozo? Never heard of it!"
 * There is one guy in the town who tells the truth, but he's of no significance until the second half of the game.
 * The boss of the area even goes so far to say that he dislikes fighting and that he'll let you pass by him unscathed. Of course, he immediately attacks you after saying that.
 * To find the Chainsaw hidden in the town, you need to Talk to Everyone to find out what time it isn't, to set the clock appropriately and open the door.
 * Similarly, on planet Dezo from Phantasy Star II, there are two kinds of Translator Microbes available. If you use the wrong one, everybody lies to you—but just like Zozo, it's absolute pathological lying.
 * On the same planet in the original game, there's a town where everyone on the eastern side will lie to you.
 * Averted in the magnificent RPG/adventure/combat thing that is Star Control II, where some rumors are true, others incomplete or false. The game is largely about figuring out (and fixing) what's been going on, and it's comfy with never giving the player a Cliff's Notes version.
 * Note, however, that all of the information you pay for is both true and relevant, if not always useful; this is because the Knowledge Brokers are much better informed than everyone else.
 * Inverted by Persona 2 where you have the ability to spread rumors and make them come true. Some of those affected are kinda confused... "I don't know what the mob is, but here's some of their stuff for sale."
 * Slightly inverted in Castlevania II: Simon's Quest for the NES. The manual warns you that what the villagers say may not be the truth. Indeed, while some things the NPCs say are true, some are only partially correct, and others are completely wrong.
 * This was originally believed to be the result of bad translation, but recently, it was found that the Japanese Script for the game was just as incomprehensible.
 * Some of the townsfolk tell you things like what Dracula's rib does or where you can find some of the thirteen "scriptures" which explain what to do at the unpassable cliffs and lakes etc. One villager tells you how to get through the poison marsh, another that it's necessary to get the cross at Laruba's Mansion... Not everything is useless or lies, and the manual does warn you that some of it is. Talking to some of the townspeople is also necessary in order to find out which ones sell you items. The dialogue sets the tone for the atmosphere and type of people you encounter in each town, deepening the game, and some of the utterances are quite funny, adding to the entertainment value. Also you know you're getting nearer the end when the townsfolk are more scared in the towns you come across, which is a useful clue and adds to the ambiance as well.
 * Of course, their lies are perfectly justified: you spend most of the game trying to resurrect Dracula, the townspeople don't want Dracula back (despite Simon only doing it so he can slay Drac again to lift a curse on himself), so they lie to you to slow you down.
 * Subverted in Nethack, the granddaddy of computer gaming. There are fortune cookies throughout the game, which pull fortunes from two massive files of information: the "true rumors file" follows this trope to the letter, while the "false rumors file" is filled with irrelevant, useless, and even dangerous information ("A cockatrice corpse is guaranteed to be untainted!"). The game also includes an Oracle, who can be paid to tell facts from the true file only, and can even be paid a massive sum to tell you major true secrets, one of which is the answer to an obnoxious Mastermind puzzle in the mid-to-late game.
 * Subverted in the ending of Final Fantasy Mystic Quest. The Final Boss tells you that the whole "legend of the chosen one" was a rumour he started...and then you go on to make him dead anyway.
 * In the Viva Pinata game, there's a character Leafos who guides you through the tutorial and gives you hints. This is brutally subverted later, as 50% of what she tells you turns out to be totally false gossip. Making this a case of Guide Dang It.
 * Played straight in Drakengard. The downside of this is that people, including members of your party, barely ever know anything about the important stuff, and it all comes in the form of speculation. The same beings can be referred to as either the Grotesqueries, the Watchers, the gods, as the characters don't know what they are and are just guessing. Anything people tell you that happens to be a concrete fact is almost completely unimportant or irrelevant.
 * Ogre Battle subverts this with Sirius. You encounter Sirius at the beginning of the Lake Jannenia level, and he tells you that the local boss is great, he's thinking about joining your rebellion, and it's best to visit him at night. However, doing so is an incredibly bad idea: Played straight in that other people you talk to will mention odd things that hint at what's behind the spoiler (one hidden town will flat out tell you what's going on, but the rest merely hint at it).
 * Also averted in the Valley of Kastro. There's a recruitable character there, and every town you visit has a different description of that character. Even the most accurate description doesn't describe that character properly (since the character is described as a member of one class, but is actually a member of another and just considered one of the first class in spirit).
 * Amusingly enough, the Sirius example has a grain of truth -.
 * Note that otherwise this trope is played straight: If a town you liberate tells you of a rumor or legend. It's 100% true.
 * The RPG Cliche quote derives from the red dragon Ruby in Lunar: Eternal Blue, who takes offense to being called a flying cat at every opportunity.
 * Exception: Ultima III was notorious for having objects mentioned in one piece of dialog that never appear within the game.
 * For that matter, most PC RPGs are immune to this trope. This is almost the exclusive province of console games.
 * Yggdra Union. Very, very early in the game, when you're touring the lands of your allies who just so happen to be embroiled in civil wars, you always hear one NPC mention a "wandering magician" who made a small contribution to the chaos. During the game's final chapter, says hello.
 * Subverted in The Elder Scrolls. In the first game, NPCs would occasionally hint to you that certain political figures in the game world were cannibals or doppelgangers. They aren't.
 * In The Elder Scrolls: Arena literally every general rumor that isn't about artifact quests is either completely false or utterly irrelevant mentions a holiday is upcoming. This would set the trend for the series avoiding it. Work rumors, which point to random quests in a settlement, are 100% accurate however.
 * A good segment of Morrowind consist of finding the correct interpretation of a prophecy, as most of the commonly avoidable ones are inaccurate.
 * Also averted with Ma'iq the Liar, who tells you blatantly false facts.
 * And then, in Oblivion, Ma'iq becomes a straight up Straw Fan, making fun of all of the major criticisms of the game on the official forums.
 * Played straight in Fallout 2. Early on, you can take a job in the den to collect a loan from a local hobo. Not only is he unable to pay the full amount, but he also immediately wants to borrow some of the money he does give you back, with a promise to return it to you at some unspecified point in the future. Amazingly enough, he will fulfill that promise, and repay you with massive interest when you return later.
 * But then averted with the Jet addict prostitute in Redding; the dialogue options make it look very much like you can do the unprovokedly saintly act and get her and her boyfriend out of Redding...but when you come back, she's still there, and Lou laughs at you for falling for her scam. In fact, in the Restoration Project at least she'll actually end up ODing if you keep giving her money.
 * Averted in GoldenEye 007. You're told that Xenia Onatopp might be on board the Frigate, so you expect to encounter her. It turns out there's no trace of her ever being there. It was a last minute change. The large helipad was originally going to be a boss fight area.
 * The horror adventure Black Mirror II features the delirious town drunk, in Black Mirror III the gamer has the option to call a fortune teller, if you decide to do so she gives you some cryptic advice which turns out to be helpful in the next chapter.