Plot-Driven Breakdown

"The Doctor: Clicking towards oblivion. How long K-9? K-9: Insufficient data. The Doctor: Yeah, you never fucking know the answer when it's important."

- Doctor Who, blooper from "The Armageddon Factor"

Sometimes things just break down purely for plot development.

It seems that even the most prepared of heroes can have their sword shatter, axle break, fuel run out, energy pack go flat or engine overheat, regardless of how well they prepared for the journey or the top-grade equipment they bought. Or a bridge or section of the cave roof will collapse at a convenient time with no apparent reason. When this inexplicable breakdown causes plot development, the item can be said to have suffered a Plot-Driven Breakdown.

Plot-Driven Breakdowns occur when a breakdown:
 * occurs at a crucial time
 * occurs for no discernable (in-universe) reason
 * causes plot development (e.g. so that two antagonistic characters end up stranded together for a whole episode, or the hero has to find another, more creative way to defeat an enemy)

Often the equipment in question is something the the hero depends on (e.g. a Plot Coupon, spiritual enhancement, The Professor's invention). Having the equipment fail is therefore an obvious way of developing the plot, forcing the hero to Take a Third Option, reassess his chances or get more creative. It's a way of avoiding the predictable "Hero defeats enemy with his favourite weapon" conflict resolution. However, when the writers fail to provide reasonable justification for the failure, the audience's Willing Suspension of Disbelief is broken.

This trope also implies the inverse notion; vital equipment will not fail or break unless it would complicate the plot.

See also Tempting Fate ("____ will save us!" Turns out it won't...). See My Car Hates Me for when this trope is applied to cars.

When this happens in video games, the player can feel like control is being taken away from them unfairly.

Anime and Manga

 * In Bleach, Ichigo's Hollow Mask is said to stay on for 11 seconds, but tends to run out just before he can finish off his opponent in the battles he loses. In the battles he wins, it stays on indefinitely after the battle is over.
 * In mecha anime Gundam Wing, Trowa's BFG arsenal on his Gundam tended to run out of ammunition at some point in a major engagement.
 * Which is probably one of the more reasonable examples, considering his battle tactics are pretty much "stand in one spot and shoot everything".
 * It's actually VERY reasonable once you realize that in about a year of nearly non-stop fighting, he only runs out of bullets about 3 times (including the movie), and each time usually after a period of intense fighting.
 * Inversion: In Naruto, when Naruto is fighting Gaara he tries to summon toads early on in battle, he gets Gamakichi and Gamatatsu (who are small, although better than the tadpoles he was summoning earlier) while trying to get Gamabunta (who's a 100 meters tall), but succeeds in summoning Gamabunta once it becomes absolutely necessary (despite the last time requiring him to use his Super-Powered Evil Side).
 * This is usually the reason that Teen Genius Susumu's experiments fail on Wandaba Style. The very first and the third are for the "no discernible reason" variety, but the others are generally due to outside interference (a fight between his pilots damages the ship, a character falls from A Twinkle in the Sky onto the electric grid, etc.). The last part of the episode is spent trying to find a way to fix the problem and not die in the process.

Comic Books

 * Possibly the Trope Maker is Spider-Man's Web Shooters, which can be guaranteed to run out of fluid whenever it's vitally needed to catch the villain (or run away, depending on the situation), forcing Spidey either improvise or (as was the case with the Green Goblin a lot) let the bad guy get away. Even when he finally wised up and started keeping spare fluid packs in his suit, that didn't stop the fluid from running out (and having to be changed) at the worst possible time. It's lampshaded. A lot.
 * As a side note, the recent movies and the several alternate continuities avert this by having the webbing be organic...except in the second movie, where a crisis of confidence shorts out his powers.
 * In the case of Empowered's super suit, it is easier to list the times when the Hypermembrane does work correctly. A justified example. Emp has a theory that the suit's reliability is tied into her self-confidence. The times the suit works are usually when she's pissed off or determined.
 * In the original (pre-movie) version of The Rocketeer, Hughes asks Peevy if anyone has thought of checking the fuel level on the rocket pack. Minutes later, Cliff runs out of fuel in mid-flight. There is exactly enough time for Hughes to get into a plane, catch up with him and grab him before he hits the ground.

Film

 * The Hyperspace Generator on the Millenium Falcon, mainly during The Empire Strikes Back, where it fails critically at just the right moment in not one, not two, but three Daring Escapes.
 * It didn't work, because it was broken. At the end, it gets fixed, and works like a charm.
 * The second time, the hyperdrive was said to be disabled by an Imperial officer.
 * It got disabled by whoever captured them every time. One would think that Han would've gotten keen to this notion by the second time, but nope, every time he expects it to work just fine and is dramatically shocked every time he realizes the Empire used the bag of tricks anybody with half a brain would utilize as a backup strategy if they were to flee.
 * Officially, it was half-working when they were flying to Bespin, despite the original intent to have the ship just fly to another system at sublight speeds.
 * Note to the Empire: Do NOT repair your prisoners' ship until they are safely off-planet. In fact, if you don't need the ship, scrap it or hurl it into a star.
 * But the Empire didn't repair it, Lando's people did. The Empire merely sabotaged it so that the Rebels couldn't escape after rescuing Luke. Vader presumably had a premonition that Luke might escape and realized that a contingency plan would be useful.
 * In the 2007 Teenage Mutant Ninja Turtles film, Leonardo suffers one of these in his rooftop fight with Raphael. Being the Turtle with the most technical skill, one would think he'd know better than to leave his katana locked in Raphael's sai - a weapon designed to trap and break swords. And upon the inevitable break, one would expect him to have a better reaction than to stare numbly at the snapped-off handles until Raph kicks him to the ground. This is probably because the key problem of the film (unity among the Turtles) would have been made worse if Leonardo had won the fight. Raphael is not the sort to be humbled by defeat and may have estranged himself.
 * This happens all the time to any source of light in Darkness Falls.
 * In the How to Train Your Dragon movie,
 * Marty is all set to go Back to The Future when the car's engine dies on him. After a successful jump (despite the technical difficultles) it dies again, leaving him ten minutes to reach Doc on foot.
 * The engine doesn't die. The starter motor does. And this was established as a problem throughout the movie. (Though one might ask why Marty and Doc don't think to just leave the thing running so they don't have to deal with it!)
 * The real life Delorean was notorious for having problems so this is also more believable.
 * Jordy shooting a cherry bomb at Jason's bike in Mystery Team.

Literature

 * Arthur's Excalibur.
 * The sword that broke when Arthur fought Pellinor was the one he'd drawn from the stone and anvil to become King. Merlin took him to get Excalibur from the Lady of the Lake. (In one adventure, Morgan le Fay had stolen Excalibur and replaced it with a copy, and given Excalibur to his opponent just before their duel.)
 * The Maghook grappling guns, from Matthew Reilly's books. After being reliable in the first couple of books, in Scarecrow The Big Guy (so to speak) finally comes across a situation where the Maghook happens to be out of propellant, and thinks "I bet this never happens to The Hero." And then in the next paragraph, The Hero has his Maghook run out of propellant.

Live Action TV

 * In the reimagined Battlestar Galactica episode Act of Contrition, a recon drone kills 13 pilots when its restraints come off seemingly on their own. It's some tragic Truth in Television, as this exact same incident had happened in reality with missiles being shuffled to their aircraft on aircraft carriers falling to the deck and going kablooie. A character in the episode even says "I know it's hard to hear, but we were lucky. If that had been a missile..."
 * Said equipment used to store the drone was also 40+ years old.
 * Red Dwarf uses this trope regularly and unashamedly, seeing as the show relies more on character interaction than plot development.
 * In Smallville, if Clark is being snuck up on and is about to be attacked in such a way as to expose his invulnerability to a regular character that doesn't know his secret, you can count on a coincidental chunk of Kryptonite popping up to make him vulnerable, or he didn't have his powers anyway. This could be more easily averted if the writers understood how Clark's super-hearing actually works and had him playing possum to protect his secret.
 * Who can forget the Transporter from Star Trek? Whenever they need to make a hasty retreat or get stuff to the surface immediately, there's always "too much atmospheric interference".
 * It gets worse: Remember the Enterprise's "transporter malfunction" in Star Trek: The Motion Picture? They even used it as a way to conveniently "remove" the new Vulcan science officer who was supposed to replace Spock. Granted, everyone was naturally wanting to see Spock on the bridge again, and any other Vulcan would most likely have been unacceptable. But come on! Couldn't they have just reassigned the poor guy?
 * Voyager was particularly bad at this, one episode (workforce part 2) had transporters and warp drive fail within minutes of each other, despite the sheer size of each system a single weapon hit is all that is required to take them offline.
 * The Stargate breaking down was, of course, the basis for some of SG1 and Atlantis's most memorable episodes.
 * DeMilo's whorehouse-on-wheels breaks down just as the heroes get to their destination in Tin Man.
 * This trope occurs in the pilot episode for Porridge, after Fletcher pees into the petroltank of a prison van.

Tabletop Games

 * In The Marvel Universe Roleplaying Game, it suggests not keeping track of ammunition. Instead it suggests using this trope. So instead of saying "Well, Spidey you have five shots of web fluid left." you let it run out like when the villain is supposed to escape, or whatever.
 * Big Eyes, Small Mouth has a similar system with the optional "Dramatic Ammunition Rules". This is coupled with an ability called One Bullet Left, that gives you one last shot when the GM declares you're out of ammo.
 * Similary the FATE role-playing system. Almost any sort of breakdown, including guns running out of ammunition, only happens when it's dramatically useful. On the other hand, the Fate Point economy means that the PLAYER may frequently suggest such breakdowns to the GM in order to get Hero Points to spend elsewhere.
 * There's also a specific stunt, One Shot Left that lets the player declare their gun is out of ammo in return for a bonus that guarantees the last shot will be plot-appropriately spectacular.
 * Mutants and Masterminds is yet another system that recommends that instead of tracking resources, users of items that care about this kind of thing suffer inconvenient breakdowns and shortages, but get a Hero Point in return for having such a complication in their description. "Equipment" takes this further and lets you acquire a power at 1/5th cost provided it can be obtained from an item mass produced and (relatively) easily purchased in the setting (or being non-portable), but, in addition to the ability to have these items lost, smashed or stolen that normally reduces the cost by 2/3rds, they can breakdown or run out of power/bullets/arrows whenever the GM likes with no compensation beyond the initial cost reduction.

Video Games

 * In Gears of War you can expect to be unable to access the Hammer of Dawn whenever a boss fight breaks out.
 * Except when you need the Hammer of Dawn to hurt it. Then there will be like six of them scattered around (despite the fact that you can't carry a second one, it never runs out of ammo in Campaign, and you can only play Co-Op with one other person).
 * In Phoenix Wright: Trials and Tribulations, Phoenix Bravely and perhaps stupidly attempts to cross a burning bridge to save Maya, only to have it collapse when he is half way across. He is sent plunging into an incredibly deadly river only to survive with little more than a mild head cold. But this accident ultimately leads to a major break in the case.
 * This is the plot behind most of the Survival levels in Left 4 Dead - they present hypothetical "What if?" situations for the crescendo events throughout the game, in which an event that must be triggered to clear/complete the path during the campaign doesn't go quite as expected (for example, in one map there is a bridge that must be lowered and crossed in the campaign, but it jams and fails to lower at all in the Survival version), leaving the survivors to simply fight until they're all dead.
 * Guess what happens if you try to ignore plot-heavy Cosmo Canyon in Final Fantasy VII? Yep, your buggy breaks down.
 * In the second half of one of the last Los Santos missions in Grand Theft Auto: San Andreas, you're given an old, poorly-maintained AK-47 to defend the car you're escaping in. About halfway through that sequence (right as the police manage to set up an effective road block) it irreparably jams.
 * This trope seems to happen in every Metroid game. Samus' powerups always malfunction or disappear somewhere whenever she needs them.

Web Comics

 * In El Goonish Shive, one breakdown of the Transformation Ray Gun caused a Noodle Incident and two other breakdowns triggered an arc leading to a new main character being created.

Western Animation

 * Captain N. It doesn't matter if he just left the palace and walked through the main gates, or if he's traveled to fourteen different worlds and then fought through 7 stages of deadly, monster-infested secret passages, his zapper/pad WILL run out of power the moment he has to fight Mother Brain.
 * Actually that didn't happen that much, but it was an easy out for the writers to force the heroes to retreat and fight another day.
 * Inspector Gadget is a walking example of this trope. He might define it better than Spider-Man does. Most of his Gadgets don't work well anyway. Although sometimes using the wrong gadget saves the day.
 * There's at least one scene (and probably two or more) in the Ruby-Spears production of the American Mega Man cartoon, where Mega Man runs low on power in a critical situation.
 * This trope is the reason Scooby and the gang ever got anything done.
 * The Mystery Machine is prone to this, it's usually the reason the gang is stuck having to solve a mystery in some out of the way locations.
 * Ben Tennyson's Omnitrix never works right. Even when it's upgraded.