A British Sketch Comedy program parodied this. A man is buying a camera, and is shown one that is "totally idiot proof". He then smashes it on the table. "What did you do that for?" "Well, I'm an idiot." The shopkeeper then shows him a camera made out of concrete.
On 9-1-1, a few of the situations shown occur due to things getting out of control.
A worker at the firehouse and his bank manager brother in law hit on what looks like a good plan for a robbery. The manager uses a drug to create what seems to be an outbreak on a money truck driver to bring the cops in. He also drugs himself and then gets locked inside the vault. While the firefighters are busy inside, the worker poses as a hazmat agent to get the other driver out of the truck. He then steals the money and puts it in the fire truck, intending to get it out later.
The first spanner is that the manager double-crosses his partner, taking advantage of being locked in to steal $6 million worth of diamonds. At the hospital, he drops a call to the cops on what happened. Thus, just as the firemen return, the cops show up to take the money before the worker can get it.
The manager then gets hit with this as he figured he'd have plenty of time inside the vault to get the diamonds. He never counts on paramedic Hen ending up getting locked inside with him. He's forced to drug her too but knows the rescue crew will be coming in faster than expected. He thus swallows the diamonds to smuggle them out...which ends up causing him a fatal case of internal failure later that night.
The owner of a failing diner decides to set the place on fire to collect on the insurance for his family. He figures by the time the fire is noticed and reported, it will have spread out to cover any signs of arson. However, his son had to go back to get his computer just as the blaze erupted with his mother calling 9-1-1 immediately. While both survive, the firefighters' early arrival exposes the arson and has the man arrested.
The Angel episode "Guise Will Be Guise" has this when a sorcerer's plan to sacrifice his virgin daughter for power is thwarted when it turns out she hasn't been a virgin since she was in her teens. She even dated one of his mage bodyguards, who probably knew that she had to be a virgin for the sacrifice to work, and shuffles awkwardly offscreen after she points him out.
Better Call Saul: Kim and Saul have been spending the better part of the last season's first half plotting a complex and large-scale con on Howard. The last step of the plan is to plant doctored photographs apparently showing Saul bribing Judge Casimiro (actually an actor dressed up to look like Casimiro). Saul is out buying a bottle of expensive tequila for the celebration on the day the prank is about to happen when he coincidentally spots the real Casimiro at the same liquor store, and he has a very prominent physical attribute which they could not have accounted for: his left arm is broken and in a sling. Realizing this means their doctored photos could be easily disproven, Saul immediately calls Kim to cancel the whole thing, but Kim refuses to quit at the last second and they quickly reshoot the scene to fix the mistake (although they have to shell out a pretty penny to get the same camera people and actor back immediately).
In the first episode of Season 2, Jesse and Walt discover Tuco is so violently psychotic, he beats one of his own underlings to death for an extremely minor slight. Fearing for their lives due to having witnessed Tuco commit murder, they devise a plan to secretly poison Tuco by lacing a batch of meth with ricin powder. Unfortunately, the plan is foiled before it can even be attempted because Tuco's other underling went to recover the body of the first underling on his own at the trash dump and ended up accidentally killing himself when the trash stack fell and crushed him. When Tuco didn't hear back from his underling, Tuco assumed he was actually a rat for the DEA, and in response kidnaps Walt and Jesse at gunpoint so he can flee with them to Mexico.
In the episode "Better Call Saul", Badger has been caught in a DEA sting operation, and will go to jail unless he can identify the mysterious Heisenberg. Jesse, Walt, and Saul set up a scheme in which (for a sizeable fee) a jailbird takes the fall for Heisenberg in a sting operation set-up. However, their plan runs into an unexpected setback when the jailbird arrives late and a random passerby who resembles the jailbird sits down on the bench next to Badger during the sting operation, making Badger mistakenly think this is the person who he's meant to rat out, while the fall guy sits on a different bench next to Badger's. Jesse and Walt have to make some rapid-fire improvising to set the plan back on track.
Blake's 7: In the episode "Weapon", Servalan brings in Carnell the psychostrategist to plot her strategy in trying to lay claim the eponymous gun from its absconding creator. (Un)fortunately, Carnell isn't informed until way too late that the scientist took a menial female slave along with him when he fled, and her presence means that all the villains' plans go pear-shaped. Carnell is smart enough to run for it himself the instant he finally hears about the slave.
In Brooklyn Nine-Nine, Captain Holt and Sergeant Jeffords begin to secretly "CompStat" the precinct office in order to meet a paperwork deadline, by secretly manipulating the detectives in order to increase efficiency. Unfortunately, both of them forgot that Detective Peralta was out of the precinct while they were doing this; when he gets back to find Detective Scully moved to his desk, Peralta shoos Scully away to the break-room, which leads to a chain of events which sees Scully accidentally start a fire and bring the whole thing crashing down around them.
In the sixth season finale, Jake assembles a "Suicide Squad" of rivals Wuntch, Stentley and the Vulture in a scheme to take down Kelly. However, Stentley's sheer stupidity keeps messing things up. At one point, Jake comes up with a scheme to fake a kidnapping with the Vulture assuring him he'll give the case to "the two worst cops in my division" to ensure it won't get solved. Too late, Jake realizes that the Vulture only considers these guys "bad" cops because they're not friends with him and in reality they're very sharp detectives who nearly ruin the plan by finding the truth.
Many a killer on Burke's Law has seen an otherwise perfect murder plan ruined by one tiny unexpected wrinkle.
The killer in "Who Killed the Highest Bidder?" would have gotten away with it thanks to his "airtight" alibi of being on a video chat in Paris when the murder was committed. But when watching the video, Burke hears a police siren in the background which doesn't match the distinctive sounds of a French police car. He thus realizes the suspect was actually in Los Angeles and faked the video call to kill the victim.
This trope has made the lives of the investigators on CSI much, much easier over the years. Whether it's people discovering a dead body before it can be completely dissolved or buried, witnesses who unwittingly provide evidence that ties a murderer to a crime scene, or a Heroic Bystander who catches a Peeping Tom that also turns out to be a serial rapist, various members of the public have helped the CSIs bring a lot of criminals to justice in many different ways.
A great turn comes in an episode of CSI: NY. A therapist plots to kill her husband and make it look like it was done by a disturbed patient who she then shot in "self-defense." When she arrests her, Stella lampshades how the woman's plan was good and might have worked thanks to the preparation; but what she could never have counted on was that when she shot the patient, a pack of cops and CSI techs would be literally across the street investigating another murder, get there in record time, and prevent the woman from properly cleaning up the crime scene.
On CSI: Miami, a bank manager and his lover conspire to trick two armored car drivers (via a faked "kidnapping") into switching their millions of dollars for counterfeit bills. The manager figured by the time anyone realized the switch, he'd be long gone with the cash. As fate would have it, another pair of crooks pick that exact day to rob that armored car, killing one of the drivers. When they're captured, it doesn't take long for the CSI team to realize the money is fake and unravel the scheme.
Generally speaking, the TARDIS from Doctor Who spends her days throwing herself, the Doctor and their Companions at various intricate plots specifically so they can act as nifty spanners, just by dint of shuttling between crisis points, whenever they may be. "VWORP-VWORP-VWORP" is generally the sound of the Villain of the Week's ten-step plan starting to belch smoke.
In "The Smugglers", the Doctor, Ben, and Polly derail seventeenth century pirates' plans to get a hold of treasure hidden by one of their number who had long since gone straight. Even if any pirates survived the final showdown, their lives were still forfeit.
In "The Pirate Planet", after all the planning to destroy the Mentiads by both a cyborg pirate captain and a tyrannical Queen Xanxia in disguise, the Mentiads and the Doctor manage to do this trope... literally.
In "City of Death", Duggan, the detective who seems to have gotten into his line of work just because he likes hitting things, derails the villain's multi-millennial scheme with one thoughtless, well-timed punch.
In "The Caves of Androzani", unusually, the Doctor's role in the story is limited to frantically attempting to get him and Peri out alive. His mere presence, however, inadvertently causes the entire messed-up Androzani society to implode under its own decay. The Doctor brings down a corrupt government by accident.
"Human Nature"/"The Family of Blood": Psychic schoolboy Tim Latimer throws a loop into the Doctor's plans to hide from the Family of Blood until their short lifespans were up by turning himself into a human and hiding out for a few months. Tim's psychic powers, you see, let him "hear" the Chameleon Arch containing the Doctor's memories and Time Lord nature, leading him to steal it after being invited into "John Smith's" office for a conversation, and opening the watch alerts the Family to the Doctor's presence.
Downton Abbey: In Series 1, Barrow's scheme to get Bates sacked by framing him for stealing gets scarpered because Molesley happens to find him stealing from the storerooms. Carson believes Molesley because as butler to Crawley House, he doesn't work at Downton itself and doesn't have the same opinions on Barrow as the rest of the staff do.
Scores of the schemes on Dynasty (2017) are marred by a huge wrinkle none of the other characters could have expected.
Alexis conspires to have a con man pose as Blake's long missing son Adam in a scheme to get her own money. But the con man gets greedy about getting his own money and thus makes a key vote that keeps Alexis from her payday.
Jeff fakes his own death and makes it appear as if Adam killed him while he leaves town. He gives the key piece of evidence to his mom to plant at the "crime scene" and thus set up Adam. Too bad Jeff never considered his mom would simply sell the "evidence" to Blake for a big check, thus removing Jeff from things while Adam remains free.
Adam himself wants to remove Fallon from the board by dredging up the lake where he overheard Fallon's old childhood friend (who died in an accident) had been dumped into. Too bad Adam had no idea there was another corpse inside the lake from another death Blake hushed up.
Fallon decides to pull a major move by selling off her publishing company to Kirby for one dollar so Blake can't get the profits of it going public, meaning Fallon makes a big payday when Kirby sells it back for the same amount. At which point, Kirby announces she has no plans to sell it back as she thinks she can run it better.
Sam plans to renovate a hotel and reopen it as a big deal. What could go wrong? First, while breaking down a wall, he finds a stack of treasure that belonged to the older owner who turns out to be famous artist. This means the Atlanta Historical Society wants to make the place a landmark which would hurt the chances of opening it as a regular hotel. Sam decides to embrace this by boasting of the artist's history...and learns the guy was a massive homophobe whose very name is considered toxic in some circles so now Sam has gay rights groups ready to picket the place.
Really, it's easier to count the number of schemes that don't go off the rails because of some spanner.
Firefly has a rare example of this happening to the hero. In "Objects in Space", River's Batman Gambit to lead Early onto the top of the ship where Mal can ambush him is almost dashed by Simon trying to stop Early, unaware that River is actually prepared to ambush Early and not simply surrendering. Fortunately, Simon's woeful lack of skill in combat means Early is able to beat him back in time to waltz into the trap.
For Life: Cassius Dawkins, intentionally sent to be so for Aaron, Safiya, and her wife, who was Maskin's opponent in the Attorney General race.
The Fringe episode "The Plateau" features a villain whose intelligence was boosted so he can perfectly predict anything that will happen and set up ridiculously complicated scenarios to kill people and escape from the agents chasing him. He's foiled by Olivia not actually being from his universe, just brainwashed to think she is. So she doesn't recognize a sign indicating a low oxygen area, and doesn't pause to grab an oxygen mask, allowing her time to dodge the stack of pipes he thought would kill her.
In the first season, the Lannisters have a very careful plan for dealing with Ned Stark in such a way that he would be discredited, but the Starks would decide against going to war, and thus the succession for the Iron Throne would be secured... and then Joffrey has Ned publicly executed for shits and giggles, causing the North to declare war and making the Iron Throne look so insecure that Joffrey's uncles Renly and Stannis both decide to take their chance and challenge Joffrey.
On a smaller scale, part of the Lannisters' plan was to take the three visiting Starks (Ned, Sansa and Arya) prisoner and use them a political bargaining chips. However, on top of Joffrey executing Ned, the much overlooked eleven year old Arya turns out to have both a swordmaster and the skills to fight back and manages to escape King's Landing. The Lannisters are left with only Sansa, and for the rest of the series have no idea what Arya's up to or even if she survived.
The survival of Arya, Bran and Rickon means House Stark isn't quite as dead as many characters believe.
In the sixth season, Margaery devises an as-yet unrevealed plan to free herself and her brother Loras from the Faith Militant. Said plan becomes moot when Cersei elects to have the entire Sept of Baelor blown up, killing Margaery, Loras, their father Mace, the High Sparrow, and dozens of others.
Indirect example but the wildfire which Aerys Targaryen left under King's Landing was a spanner in the plans the High Sparrow had to establish the theocracy in Westeros and ultimately leads to his death.
Also in the sixth season, Littlefinger's long-running plan to make Sansa Stark his new bride and turn her into a puppet Queen of the North is suddenly dashed when Lyanna Mormount decides to shame the various Northern factions into naming Sansa's "brother" Jon Snow the new King of the North.
Ramsay to his own father. While Ramsay takes orders from Roose, he does things Roose doesn't order and in doing so screws up Roose's plans. For one thing, there's burning Winterfell and flaying the Ironborn, when it seems Roose's offer to them of safe passage out of the North if they surrendered was genuine. Not to mention that Theon's value as a prisoner became virtually non-existent after Ramsay castrated him; Balon has no use for a son who can't continue the family line. When Roose has Ramsay use Theon to have the Ironborn at Moat Cailin surrender, the plan almost collapses because Theon is so emotionally broken that he can't command respect from them.
Roose: Ramsay delivered the terms. The Ironborn turned on Theon as we knew they would. They handed him over, trussed and hooded, but Ramsay... well, Ramsay has his own way of doing things.
Thanks to the High Sparrow's manipulations, Tommen ruins whatever plans Cersei and the Small Council had to curb the power of the Faith Militant.
Daenerys to the whole Game of Thrones, as per Varys. The original plan was for Dany to marry Khal Drogo to provide Viserys an army to take Westeros in place of dragons, but Dany's assimilation into the Dothraki, her supplanting of Viserys in their hearts and minds, and then finally her hatching three dragons upset all of his and everyone else's schemes. Nobody expected or predicted that Daenerys would do the things she did or become the great conqueror and liberator she has.
Stannis Baratheon's arrival at the Wall completely derails Mance's invasion, but also throws a wrench in Roose Bolton's attempts to solidify the North under his rule.
Renly's rebellion was one of the key factors for why Westeros was divided in the wake of the Succession Crisis after Robert's death. Ned wanted a smooth transition to Stannis over the illegitimate children, yet Renly insisted that Ned leapfrog the line of succession and make him King for ideological reasons which Ned refused and in response, Renly, Loras and their contingent of soldiers leave the capiital. This prevented Ned from having proper allies at the key moment of Robert's death, forcing him to turn to Littlefinger and Janos Slynt instead, leading to his downfall. In addition, Renly declaring himself a King was a key factor in the Succession Crisis becoming a War of Five Kings, rather than a straightforward conflict between Joffrey and Stannis as Ned intended. Since Stannis hadn't yet received Ned's letter he didn't know of his claim until much later. Renly declaring himself King challenged the line of succession, as Robb Stark pointed out, which led to the North and Riverlands electing Robb as King in the North. Had it not been for Renly, the North would have probably rallied behind Stannis as Ned intended, and there would have been a proper alliance against the Lannisters.
Daenarys' invasion of Westeros begins with seemingly one-sided odds; with her, the Tyrells, the Dornish, and part of the Greyjoy fleet, along with an army of Dothraki and Unsullied, versus the Lannisters and a small handful of supporting lesser noble houses. Enter Euron's alliance with Cersei, where he destroys Yara and Theon's fleet and abducts Yara, kills or captures Ellaria and the Sand Snakes, and destroys the part of Dany's fleet at Casterly Rock. Euron manages to pretty-much singledhandedly save the Lannisters from losing the war.
Arya returning to Winterfell ultimately becomes the death blow to Littlefinger's plans, and Littlefinger himself. He works on the assumption that Arya would want to usurp Sansa's place as Lady of Winterfell, and uses this to play the sisters against each other. He fails to realize she couldn't care less about being Lady of Winterfell and only wants to protect her family and take revenge against those who'd wronged them, the former part at least being something Sansa is well aware of, allowing the sisters to work together to trick him into a trial where Arya promptly executes him.
Get Smart, of course; Maxwell Smart is more likely to defeat KAOS by accident than on purpose.
The main characters in The Good Guys are generally competent cops (yes, even Dan Stark) who solve major crimes largely by stumbling into them while investigating something much smaller.
The Antichrist is born, and an order of nuns in service of the Devil are preparing for an American diplomat's wife to arrive at their convent in labor. They will then switch her baby for the Antichrist as growing up in an influential American political family is the first step toward achieving his destiny. What throws it off is that a couple called the Youngs show up with the wife also in labor. When Crowley drops off the Antichrist, Mr. Young tells him that "the birth" is happening in Room 3, meaning his own child. But Crowley thinks he means the diplomat's wife and so gives the child to a nun to switch. Then two nuns each misinterpet the other's winking signals so instead of the diplomat's family, the Antichrist is given to a totally different couple. So when Crowley and Aziraphle decide to stop Armageddon by finding a way to "defuse" the Antichrist, they have no idea they're dealing with the wrong child and so, 11 years later, this mix-up nearly ends the entire world.
As it happens, the boy, Adam, turns into a spanner for Armageddon. Had he grown up as a diplomat's son, he'd have turned into a spoiled and obnoxious brat who'd be a nightmare with his powers. Instead, he grows up with a kind family and, more importantly, a group of friends who tell him off when he tries to use his powers for wicked stuff. This group of kids ends up aiding Adam in stopping the Apocalypse. Aziraphle even lampshades it by dryly noting to Crowley how things would have ended poorly "had we been more competent."
The big move of the Four Horsemen is to set up a computer virus to cause a worldwide nuclear missile launch. Walking Techbane Newt, whose presence no one but an ancient seer saw coming, hits one command into a computer and the entire program shuts down to prevent the launches.
The entire premise of the first season is that the Good Place architect is finding his carefully constructed paradise, tailored to perfectly meet the needs of each inhabitant, is suffering cataclysmic disasters. He knows that something is a Spanner in the Works but he does not know that it is Eleanor, who was sent to the Good Place by mistake and her actual selfish nature and behavior is apparently incompatible with the very nature of the place.
The above is actually a subversion: Eleanor and her three 'friends' have actually been in The Bad Place all along with the intent of them believing that they were in heaven while their insecurities and clashing personalities serving as an eternity of psychological torture. Those disasters were deliberately engineered by the architect to make Eleanor fear being exposed as a fraud. However, he did not count on Eleanor undergoing genuine Character Development and his entire plan goes Off the Rails when she selflessly confesses that she does not belong in paradise.
Also, Michael ends up becoming the Accidental Hero of the whole series by simply doing his job. He proposes a new neighborhood in the hopes of impressing Shawn and revolutionizing torture, only to learn that humans are capable of change after death and keep improving no matter what he does to gaslight them. Then he learns that the system is so forked up that no one can enter the Good Place, exposing that Shawn was enabling a broken system. Cue Michael facing bureaucrat after bureaucrat in the divine hierarchy, before he and the Soul Squad convince Gen that something needs to change.
Harrow: In "Quam Innocentum Damnari" ("An Innocent Man Is Punished"), after killing the Victim of the Week, the murderer comes up with a brilliant scheme to frame the victim's lover for the crime. What they did not know was that the lover was already dead at the time the murder took place.
On Hawaii Five-0, a mystery novelist appears to have been almost drowned in her tub by a man out for a secret lost novel. The open air duct indicates he escaped that way. Later, Steve and the others come up to reveal how they figured out this whole thing was a massive publicity stunt for the novel which got out of hand (including a couple of real murders). Steve compliments the author on the whole thing but notes how there was one major flaw: the air duct had been sealed off for repairs to the above floor so there was no way anyone could have escaped through it. When they found this (literal) dead end, it didn't take long for the cops to unravel her entire hoax.
In the first volume of Heroes, there was a large and complicated plot that involved blowing up New York in order to usher one of the characters into the White House. The only thing stopping it from being a Gambit Roulette was the fact that the people responsible were basing their convoluted plot on the works of an artist who could paint the future. And it was working, hell, it almost did work. Unfortunately for them, a certain Future Badass with the power to control the Space-Time continuum didn't like the result, and traveled back five years to give a message to one of the present day characters. This guy had no idea that there was any sort of plan, he just thought it all happened naturally, but the message he delivered set off a chain of events that ended up ruining the plan at the last minute.
In The Incredible Hulk (1977), David Banner is a 2-in-1 spanner: he tends to accidentally stumble into some illegal activity going on. When the bad peoplein each episode try to get rid of him using violent methods, it leads him to transforming into the titular character, who is a big green spanner that ruins the schemes for good.
Shinji Kido/Kamen Rider Ryuki is this trope's personification when it comes to Kamen Rider. He has an unholy ability to barge in at the least convinient moment and his The Determinator tendencies make him impossible to remove from the plan once he gets there. Also, being an Idiot Hero, he doesn't know any of this.
Shotaro Hidari, despite being the main character of Kamen Rider Double, gets this from every single one of the show's Chessmasters. Neither Ryubee Sonozaki nor his wife Fumine, AKA Shroud, ever considered that the overly emotional and all-too-human detective could possibly be a factor in their plans, especially since Ryubee's Terror Dopant form emits such raw Primal Fear that Shotaro can barely think in his presence, and Shroud was planning on partnering up Ryu Terui (Accel) with Philip since they're both immune to that effect. Neither did the True Final BossJun Kazu, the Utopia Dopant, thanks to his Reality Warper powers. Shotaro manages to show them all up, overcoming his limitations with a combination of Hot Bloodedness and loyalty to his True Companions that lets him make the impossible possible, even defeating Utopiawithout transforming into Double. Arguably lampshaded by Shotaro being tied heavily to the concept of the Joker — he's both the Wild Card (the element nobody saw coming) and the Trump Card (the key to victory).
The Season 10 finale, "Zebras", had this in the form of a mosquito, of all things. It had been killed in the same gas attack that had killed the perp's lawyer and everyone knew it could reveal who the killer was. What they didn't realize was that the killer wasn't who they thought it was.
This is why Nate has to be a master of Xanatos Speed Chess. All it takes is for, say, the mark to make a change to his daily routine or an unexpected phone call or a sudden visitor to pop in and it can throw the team's carefully planned scam off.
Sometimes, the spanner comes from the discovery the mark is more dangerous than the team thought. For example, their simple con on the corrupt owners of a Chinese laundromat goes awry when they find out the place is the front for the Triads. Likewise, a sting on a Russian businessman at his daughter's wedding is thrown when they discover too late the guy is connected to the Russian mob and half the wedding party are ruthless mobsters.
Another spanner can be the team's amazing ability to hit Gone Horribly Right on their jobs. In more than one case, they con the owner of a corrupt business into thinking it's in jeopardy, expecting him to sell it off to them...and instead the owner just decides to shut the business down and put everyone out of work.
On at least one occasion, the team hit a wrinkle they never expected: their mark is actually a downright decent and good person who's simply made mistakes, not some corrupt monster so have to adjust the plan so as not to ruin them.
"The Beantown Bailout Job" has the team up against The Irish Mob on a job and using the nebbish local bank manager as a pawn. It's only deep in the con that they discover the manager is, in fact, the mastermind of the entire scheme.
In "The Gold Job" Hardison demands, and is given, the opportunity to run his own con by Nate. Hardison plans an elaborate Batman Gambit based on video game theory and it's working very well, until the people he's manipulating decide that it's not worth the effort to keep jumping through his hoops. In an ending scene Hardison receives a letter Nate wrote earlier in the day which outlines the three things the plan needed to succeed (which Hardison's plan made possible). Nate then explains how he plans his cons to anticipate the possibility of spanners; he starts with the crude, ugly basic plan, and then plans the elaborate, beautiful, intricate plan from there.
Nate: The perfect plan, it's got too many moving parts, too much that can go wrong. You have to expect the perfect plan to fail, that's what I do.
"The Office Job" has a straight-up scam to bring down Fred Bartley, the owner of a greeting card company who the team believe is scamming by creating fake orders and pocketing the cash. Spanner 1: There's a crew filming a documentary and naturally, having a camera crew around makes it harder for the team to pull their scam. Spanner 2: They realize this isn't embezzlement, someone is using the company to print Counterfeit Cash. And Spanner 3 is Fred is really a nice guy just in over his head and it's his supposed trusted aide who's the real crook and using him as the fall guy.
Also seen in "The Tap-Out Job"; Nate is pretending to be a fight organizer from South Dakota, complete with a convincing online profile. The Spanner comes in the form of the mark's assistant. He gets suspicious and calls his cousin Jimmy in South Dakota, who "knows every fight producer in the state", but never heard of Nate's alias.
Hardison: Look, you know what I can do? I can re-task a satellite. I can get a level-3 NSA security clearance. But I can't hack a hick.
"The Rashomon Job" features the crew each trying to claim that they were the one who stole a priceless dagger from a museum years ago. However, it turns out that none of them got the dagger in the end because this trope was in play. Everyone's plans collided with each other, resulting in the dagger quite literally falling into Nate's hand.
The sequel series shifts it up as, without Nate, the team is less prepared to handle and adjust to such spanners. "The Card Game Job" is nearly ruined when the reclusive millionaire not seen in years suddenly shows up at the event. "The Tower Job" has the team thrown when the wife of the corrupt builder waltzes into the empty floor they were using as a hideout to have a fling with her assistant and recognizes them all.
In "The Bucket Job," the team do a nice act by giving a dying librarian a role in a "spy" adventure. What could go wrong? A batch of real spies showing up for one...but then when this quiet, mild-mannered librarian suddenly breaks away from the plan because he's a retired spy himself who doesn't know what's real and what's part of the game.
"The Harry Wilson Job" has the team running what should be a simple con until they keep getting interference. It turns out that the long-absent Hardison has his team working a con on the same mark and the ensuring Gambit Pileup nearly ruins it all.
"The One Man's Garbage Job" has a simple con as Sophie poses as an insurance investigator asking corrupt smuggler Hammond for paperwork on his art. As the team figures, he won't have it and his offering a bribe to Sophie will set up his fall. They're naturally rocked when Hammond immediately offers up the paperwork and realize he has a forger on his side. Then it turns out that said forger is Sophie's old "friend" Arthur, whose knowledge of her tricks keeps shuffling the plan even when they try to bring him on board.
In Malcolm in the Middle, Malcolm's dad Hal is accused of being the mastermind of a money-laundering scheme in his company, which was set up by his corrupt coworkers to make Hal the fall guy. Unfortunately, the culprits made the mistake of claiming they witnessed Hal doing the money laundering every Friday... except Hal has been skipping work on Friday for the last 15 years to go and have fun, with proof of his adventures.
Married... with Children: Kelly Bundy tended to mess up whatever plan she became involved in, given her role as The Ditz and Brainless Beauty. It's even lampshaded by Peggy at one point as the Bundys and the D'Arcys are being arrested by the police, when she notes that it probably wasn't a good idea to let Kelly in on the plan.
Dale J. Biederbeck III was rich and influential enough that he could get away with whatever he wanted. Then Monk's investigation allowed the police to arrest Biederbeck's personal physician, whom Biederbeck had blackmailed into service. Said physician immediately agreed to provide as much information as he could to get Biederbeck arrested as well.
In Biederbeck's second appearance, he's the spanner in another murderer's plot. The victim was a death row inmate who would have died anyway, and when suspicion fell on Biederbeck, the prison staff stalled on completing his Luxury Prison Suite. Monk was about to walk away, not wanting to stay in the prison, but Biederbeck promised him vital information on his wife's murder in exchange for solving the case. Monk agreed, and with his skills, the murderer and motives were exposed.
Tragically, Lancelot became this for Arthur and Guinevere on Merlin despite repeated promises to himself and Merlin that he would never come between them. However, Morgana resurrects him after his Heroic Sacrifice, robs him of his free will, and forces him to seduce Guinevere (who was enchanted to respond to his advances).
In Oshin, Oshin's very meddling mother-in-law Kiyo plans to part her from her son Ryuuzo when she leaves Saga to work in Tokyo, by intercepting Oshin's letters and cutting off her and Ryuuzo's communication. The plan works very well when Oshin moves to Sakata, stops getting Ryuuzo's letters (since he doesn't know she has moved away) so she thinks he's ditched her and vice versa, until two people ruin this: Oshin's other prospect love interest Kouta (who writes to Ryuuzo to call him out on his "abandonment" and say he will help Oshin and her son Yuu instead, making Ryuuzo realize there's something fishy going on) and Ryuuzo's sister-in-law Tsuneko (who finds the remains of Oshin's letters, reconstructs them and shows them to Ryuuzo).
Every killer on Poker Face quite likely would have gotten away with their murder scott-free if only Living Lie Detector Charlie hadn't picked just this time to be on the scene and soon figuring out what really happened.
Mighty Morphin' Power Rangers: In Season 2, "When Is A Ranger Not A Ranger," Lord Zedd makes a monster out of a kaleidoscope to erase the Rangers' memories and suppress their powers. He gets half of them, allowing the other half to figure out that using prisms can reverse the process, but Scatterbrain still manages to erase their memories. But Bulk and Skull saw the whole thing, and when Scatterbrain is about to finish them off, they grab the prisms and confront the monster. Scatterbrain zaps them, and while it costs them their long-sought-after memories of the Rangers' true identities, the prisms reflect the light into the Rangers and restore their memories and powers.
Zedd: Leave it to a couple of meatheads to mess up my plan!
Power Rangers Ninja Storm begins with Lothor ambushing all the ninja schools (ninja being the only ones who could stop him) and capturing the students. Only five people manage to remain: the Wind Academy's Sensei (who was not captured, but was effectively neutralized by being turned into a Guinea pig), his son Cam (who wasn't captured because he wasn't a student), and three student ninja who decided to be good samaritans and so were Late for School. Since they were the only ones with anything resembling the proper training, the three students ended up becoming the new Power Rangers under the mentorship of the Sensei and with Cam's help, and soon they start fighting back against Lothor.
Power Rangers RPM: Venjix's plan to infect Corinth's population with half-human hybrids and then conquer Corinth in one fell swoop would've gone off flawlessly, had it not been for General Kilobyte being jealous and activating a hybrid, Hicks, early and attempt to kill Scott and Colonel Truman, thus tipping the Rangers off about the plan (Venjix banishes Kilobyte in response).
In the third series of Primeval, Helen has a plan to kill the first hominids and thus erase humanity from existence. She very nearly succeeds, if not for one desperately hungry raptor.
The fun of Prison Break is how Michael has crafted an intricate and brilliant plan to break his brother Lincoln out of a prison. It includes tattooing the blueprints on his body and crafting perfect escapes. From day one, Michael learns the hard way that real life has a way of throwing wrinkles into any plan...
The biggest failing is Michael realizing too late that people in prison don't react the way normal people would. He had assumed he could just win over mobster Abruzzi by offering the location of a witness against him after they escape. He doesn't expect Abruzzi to simply order his goons to torture Michael for the information.
A major part of the plan is how Micahel is convinced Westmoreland is legendary hijacker D.B. Cooper and his hidden money is key to the escape. Too bad Westmoreland has a perfect alibi for when Cooper's hijacking took place. Subverted as a dying Westmoreland does confess he was indeed Cooper.
Michael thought it would just be him, Abruzzi, Lincoln and Westmoreland escaping. But soon, various others find out what he's up to and the escape crew expands beyond Michael's planning.
The initial escape looks to be going great and just like Michael planned...until he discovers that the water pipe that he weakened to create the escape tunnel has been replaced by a new and stronger pipe that's impossible to break through.
Michael had planned just a minor distraction for the initial escape...only for it to turn into a full-blown prison riot. During which, dangerous psychopath T-Bag stumbles onto the plot and forces his way onto the team which creates numerous spanners down the road.
The gang track down the money Westmoreland/Cooper buried long ago...only to find the area is now a housing development. They get into the target house and are forced to hold the owner hostage...at which point, her police officer daughter drops by for a visit.
Michael prides himself on being smarter than anyone the FBI could send after them. He could never count on the FBI handing the case to Alexander Mahone, a brilliant agent whose quirky mind allows him to figure out just what Michael is up to.
Perhaps the biggest spanner of all is that Michael went into this under the impression that Lincoln's conviction was simply the justice system getting the wrong man. It's only deep into the plot that the brothers discover Lincoln was set up by a powerful conspiracy who counts the Vice-President of the United States among their number. Michael lampshades how he was prepared for the cops and feds but not a group who can commander the resources of intelligence agencies to hunt the brothers and doesn't care who they have to kill to get their own way.
Really, about half the series is all about Michael's "perfect" plans going awry.
Psychopath Diary: Dong-sik constantly ruins In-woo's plans just by existing. Shown especially when In-woo is about to murder Bo-kyung, then learns Dong-sik has got the police looking for Bo-kyung.
Salem: John Alden's mere presence in Salem is screwing up the witches' preparations for their Grand Rite. Increase Mather later becomes this as he basically appoints himself the inquisitor of Salem.
Stargate SG-1: SG-1 was once called to help Thor to serve this very purposenote Actually a subversion: the Asgard didn't need stupid people, they needed people who thought very differently from the Asgard, as the Replicators were perfectly capable of countering Asgard attempts, but had no experience with humans.
Jack O'Neill: So what you're basically saying is you need someone dumber than you? General Hammond: I'm sorry, Thor, but we need SG-1 here. Sam Carter: I could go, sir. Jack O'Neill: I dunno, Carter, you may not be dumb enough.
In "2001", A simple Volian farmer gives a glowing account of the Aschen, being completely ignorant of what they did to his planet, and sees no problem asking Daniel and Teal'c for help with the "iron root" in one of his fields. This ends up completely undoing the Aschen's plans for Earth.
"The Trouble with Tribbles" from Star Trek: The Original Series. A Klingon spy going by the name of "Arne Darvin" poisoned a shipment of quadrotriticale grain being sent to Sherman's Planet with the intent on preventing the Federation from claiming it. However, a shady trader named Cyrano Jones had arrived at Deep Space K-7 with small alien creatures called Tribbles in tow. Tribbles eat everything in sight and multiply extremely quickly when fed. The Tribbles quickly breed out of control and get into the grain stores... at which point they die from the poison, which causes the humans to realize that something was wrong and find out what it was by autopsying the dead Tribbles. The Tribbles also expose Darvin due to their mutal negative reactions with Klingons.
"The First Duty", Wesley, his buddy Nicolas Locarno, and their squadmates at Starfleet Academy, were involved in a flying accident that got one of their friends, Joshua Albert, killed, and their resulting testimony given to Starfleet officials is a bit shaky on the details. It seems as though Joshua simply made a fatal mistake while piloting his aircraft, and Locarno would've been content to let that be the story. Unfortunately for him, Captain Picard and the Enterprise crew got involved with the investigation, out of loyalty to Wesley, one of their own. This is when Picard found out what really happened: Nicolas Locarno convinced Wesley, Joshua, and the others, to perform an illegal maneuver for their flight demonstration, and it didn't work as planned, killing Joshua in the process. Picard then gives an epic What the Hell, Hero? speech to Wesley in the ready room, after which Wesley, utterly ashamed of himself, blows Locarno's cover at the following inquiry.
In "Starship Mine", the Enterprise is cleared of all personnel so a baryon sweep can clean exotic particles out of the ship. Right as Picard is about to leave the bridge, a maintenance crew assemble on the bridge to do their part in cleaning up. At a small party down at the starbase on the planet below, Picard does not like having to put up with Commander Hutchinson, who is every single guy at a party who just yammers on about nothing. Seeking an excuse to leave, Picard claims he's going to quickly grab his saddle from the ship and go horse-riding. And in doing so, he discovers the "maintenance crew" on the Enterprise are actually criminals stealing trilithium from the ship, none of whom expected Picard to return to the ship, figure out what's really going on, and go all Die Hard on the Enterprise on them.
The two-part "Improbable Cause"/"The Die Is Cast" has Enabran Tain, former head of the Obsidian Order, organize a joint operation with the Romulan Tal Shiar to make a preemptive strike on the Founder homeworld. It's a well-detailed plan headed up by arguably the most brilliant mind the Order has ever seen...and it fails because Tain misses how one of the chief Romulans has been replaced by a Changeling. Thus, the strike turns into a trap wiping out the Order and Tal Shiar forces.
"The Assignment"; when Keiko is possessed by a malevolent alien called a Pah-wraith that threatens to kill her if O'Brien doesn't perform some "adjustments" to the station, O'Brien recruits Rom to help him. Rom's surprising grasp of what the "adjustments" would do to the station ("Why are we trying to kill the wormhole aliens?") and his knowledge of Bajoran mythology and folklore from his conversations with Leeta end up giving O'Brien the key he needs to thwart the Pah-wraith's plans and save his wife.
Seska's cover story in Star Trek: Voyager as to why she has Cardassian blood factors despite ostensibly being a Bajoran (she received a bone marrow transplant from a sympathetic Cardassian to cure a childhood disease) might have passed muster when dealing with any ordinary doctor or field medic. But Voyager's doctor is the ship's Emergency Medical Hologram, who is essentially a walking database of all recorded medical knowledge in the Federation, so he instantly knows it doesn't work that way.
In Heroes Vs. Villains, Tyson served as a Spanner In The Works for Rob's gambit by serving as an Unwitting Pawn in Russell's gambit. The Villains tribe was divided between Rob's and Russell's supporters, with Rob leading 6-3. However, Russell had an immunity idol, which meant that when the tribe voted someone out, he (or whoever he gave the idol to) could stand up and play the idol to prevent any votes cast against them from counting. Rob wasn't sure whether the idol would be played by Russell or by Russell's closest ally, Pavarti, but Rob had a plan to guarantee they could get rid of either Russell or Pavarti. He would have three people vote for Russell and three for Pavarti; then, regardless of who played the idol, the other one would have three votes. Even if all three people on Russell's side voted for one person, it would have meant a 3-3 tie between votes to get rid of Russell or Parvati and votes to get rid of whichever Rob supporter Russell targeted, leading to a tie-breaker that Rob's side could easily win. However, the plan fell through because Tyson actually let Russell (his alliance's enemy) tell him who he should vote for. Rob had assigned Tyson to be one of the three people to vote for Russell. However, Russell told Tyson that he would sacrifice Pavarti and use the idol to protect himself, leading Tyson to think that he should vote for Pavarti because votes against Russell wouldn't count after Russell played the idol. Russell had other plans, and gave the idol to Pavarti. After the votes were cast, Pavarti played the idol, meaning that the final vote count was four votes (including Tyson's) against Pavarti that didn't count, two votes against Russell, and three votes cast by Russell and his allies against... Tyson. It was three to two, and Tyson was sent home. Afterward, Tyson admitted to the camera, "I am a victim of my own stupidity." His action was one of five official nominees for the dumbest action in Survivor history.
Sash fell victim to three Spanners during Nicaragua. He was in a very good position in the game, having just ousted Chessmasters Marty and Brenda in quick succession, but then his closest allies Kelly and NaOnka decided to quit at the same time, leaving him without an ideal final three (Kelly did very little in both strategy and physical play, and NaOnka was universally disliked by the other tribemates). He managed to quickly get himself into a secret alliance with Chase, Holly, and Jane, but then Fabio, who was both the alliance's obvious target and had been faking the part of the Dumb Blonde up until that point, planted the idea in Chase's head that Jane needed to be taken out before anyone else. Sash proceeded to make the plan his own, which in turn led to Jane revealing the alliance at the next Tribal. From there, Sash could only helplessly watch as Fabio went on a string of Immunity Challenge runs, keeping him safe to the very end, which forced Sash to turn on his alliance and vote out Holly. The end result? A Final three of Sash, Chase, and Fabio, with Chase getting four votes, Fabio winning with five, and Sash with... none at all.
On S.W.A.T. (1975), a group of crooked cops prepares a scheme to rob a beauty pageant of the million-dollar diamond crown and scepter to be given as a price. They've got it all set to pose as security guards, get the jewels, it's working perfectly...then one of the cops realizes the jewels are fake. It turns out the pageant owners had swapped them with duplicates, intending for the security guards to get blamed for missing jewels while they ran with the real ones. The ensuing fight over the real jewels turns into a hostage situation before the cops arrest the entire bunch.
In an episode of Wallander, the title character avoids a fatal bullet by tripping over a conveniently-placed rug.
The Season 5 finale of Weeds features an unusual instance of a smart character acting as fate's tool: Shane Botwin's murder of Pilar, a brilliant criminal who acted as puppeteer for Estaban, the Mexican stock exchange, and Mexican government as a whole. Essentially, Shane and his croquet mallet accomplished in a mere second what Nancy and Guillermo had failed to do in half a season, and those two burnt down an entire town without getting caught...
In White Christmas, Kang Mi Reu sneaks back into the school unbeknownst to anybody but his fellow students to pull a prank after being expelled. The killer never knew he existed and when he reveals himself and holds the other kids at gunpoint, Kang Mi Reu had since left the school. Though unable to navigate the snow Mi Reu returns and tries to pull a prank on an unsuspecting person, in actuality the killer, by wiring a doorknob to shock him. It disables the killer long enough for them to get the gun away from him and reclaim the school. Only then does he realize that a dangerous serial killer had been threatening everybody.
A woman is able to use a hypnotic power to control any man. She naturally can't understand why "Jacques" appears immune to her charms to ruin her plot.
The Chameleon is able to "bend light" to look like anyone and impersonates "Jacques." D'Artagnan (the only one who knows her secret) can see it through because the Chameleon is acting like an actual man, not a woman pretending to be a man.
The Chameleon is also thrown when Captain Duval "confesses" to a crime the Chameleon committed as part of his plan to flush the imposter out.
