Buffy: And that would be what?
Spike: One good day.
As Long as There Is Evil, good must rise to the challenge and defend the world. Beating the Big Bad and his pawns will maintain the Balance Between Good and Evil and keep the world safe. Good doesn't always win, however, whether it's Stage One of the Evil Plan or in the final battle, heroes do occasionally lose. In these cases, the old heroes, or a group of new ones, must again rise to challenge the bad guys, usually with better results.
In some stories, this won't happen because The World Is Always Doomed. Evil only has to win once in order to permanently turn the world into a crapsack Villain World with absolutely no hope of being deposed. Heck, if the villain is an Omnicidal Maniac there won't even be a world to save. It's one of the justifications for X Must Not Win (in this case, X is the villain).
When Evil Only Has To Win Once, heroes need to step up their game because the Sorting Algorithm of Evil just divided by zero. Usually this shows up in stories where there is some kind of repeating challenge against the forces of good; be it a martial arts tournament for control of the planet, a resurfacing Sealed Evil in a Can, or just a laundry list of progressively more dangerous enemies. You can expect The Chosen One to feel the pressure — there are hundreds of mooks, dozens of mid-level bad guys, a Dragon, one Big Bad villain — and one Hero (or a team, but you get the idea) to face the threat. There's no one else to face the threat... usually, at least. Hopefully the replacements can do the impossible.
Either/Or Prophecies use this trope with language along the lines of "If Dark Lord Genericide finds the Ruby Heart he will bring about a thousand years of sorrow!" Rarely, the prophecy's "Or" has the heroic variant included: "... but if Sir Tropesalot finds the Sword of Plot Advancement, he will take up the crown and usher in a thousand years of peace!"
It just doesn't seem fair. Why is it that beating the Big Bad doesn't bring about a thousand years of perpetual (hopefully not literal) light? There's two potential justifications for this: Good, true Good, won't stoop to the levels necessary to create a permanent Sugar Bowl, whereas Evil won't have a problem with completely wrecking the world. The other reason is that the Good Guys are usually the only ones concerned with maintaining the Balance Between Good and Evil. Metatextually, the Author also probably wants a world where his Chronic Hero Syndrome-suffering protagonist can't sleep. Also, we know Villains Act, Heroes React, and an action can often be tried many times until successful.
True in pretty much all video games. You have to win through every challenge you face to get to the end, whereas your enemies just have to win once and (unless it's a Hopeless Boss Fight or Final Boss Preview) it's Game Over (This is why an ability with a small chance to utterly ruin the target, but leaving you exposed or weakened if it fails, quickly becomes a Useless Useful Spell). It's also frequently inverted in the form of an Instant-Win Condition, from the perspective of a player stuck against That One Level or That One Boss; no matter how many times you get beaten down, you (generally) only need to win once in order to progress. This trope may also be the reason why No Canon for the Wicked is commonplace.
- In Neon Genesis Evangelion, if even one of the Angels penetrates the heart of the NERV base, Third Impact will be initiated, wiping out all life on earth. Technically, an Angel already penetrated the NERV Base... since before the start of the series. Said Angel is actually Humanity itself and they're also trying to initiate Third Impact. And they're the ones that succeed. This is one hell of a Crapsack World, huh?
- Elimona from Defense Devil once stated that this was not the case, despite how it seemed, since the Devils are dominated by the Angels and are at the verge of destruction anyway. The Angels are just waiting for the two strongest demons, Legato and Kucabara, to defeat each other so that they can easily purge the world of demons and devils.
- In MÄR, the world hasn't been living the best of times because, while the Chess didn't lose the first fight, the good guys also didn't win, and the leader of the bad team escaped, so the world's been living in fear of the Chess rising again. Doesn't help that their captain (not the leader though) was a zombie and the world was told that he'd be back after a while, so they've been living in fear for the second War Games to start, which is where the story begins.
- Furthering this trope is the fact that if the captain of either side loses, that side loses the entire game. The Chess have an entire army, so their captain stays out of the fighting until the sorting algorithm of evil forces him to join in. Team MAR only has one or two extra players, forcing the captain to participate in almost every round.
- Bleach: If Tsukishima so much as nicks you just once with Book Of The End, the fight is over - simple as that. It doesn't have anything to do with being a One-Hit KO, rather it's a twisted form of Mind Rape with a healthy helping of Reality Warping: Anything Book Of The End cuts lets Tsukishima alter its past, person or thing. Therefore, cutting somebody lets him insert his existence into their past any way he likes, such as a family relative, best friend, or cherished mentor. In short, he strips the enemy of their will to fight him, and can even alter it so that they fight for him. Though it fails against Byakuya, who is willing to kill him despite the false memories.
- In Mobile Fighter G Gundam, Domon cannot lose a single round of the tournament, not even a qualifying round, as it would disqualify him from being able to fight and stop his mentor Master Asia from using the Devil Gundam, as Asia is sitting at the top of the tournament.
- In the Yatterman series, Gan and Ai could beat back Dokurobei's forces with some difficulty, but ultimately kept Dekkaido safe. It took multiple continuities before Dokurobei got really, really pissed off, but in Yatterman Night he exiled his lovable minions and took to destroying Dekkaido himself, becoming the ruler of the charred remains of the world and making everyone's life a living hell.
- Used as a villainous encouragement in My Hero Academia. When Tomura Shigaraki fails to defeat the heroes, his mentor All For One assures him that he can just try again and again until he succeeds. While the heroes clearly won the encounter (taking out All For One, a large number of Nomus, and driving Shigaraki into the ground), they realize that with Shigaraki on the loose, he's just going to build up his forces and attack again.
- There's a version of this in The Transformers: Last Stand of the Wreckers: Shockwave tells Overlord that he isn't the first Phase Sixer (or One-Man Army) to bait Megatron. Overlord notes that he only has to be the last — the one who wins. And while in this case both parties are evil, Overlord is probably the worst of the two.
- The backstory of the original Mark Millar comic book Wanted. The premise of the setting is that the supervillains of the world finally decided to all team up and thus overwhelm the superheroes by sheer numbers. After their victory, the villains used one of their Reality Warpers to retroactively change reality so that the heroes became normal people (with ironic twists to their lives), and they themselves were set up as the secret rulers of the world. The only hint that anything was ever different is the existence of superhero comic books, which represent the ultimate victory of the supervillains — although the comics depict actual events from the previous reality, nobody would ever take them seriously.
- In one Batman: Gotham Adventures comic, the Joker claims that he's always let Batman win because if the Joker wins once, Batman dies and can no longer be played with, but every time Batman wins, the Joker is simply sent to Cardboard Prison and it's only a matter of time before the game begins again. Of course, this is the Joker talking.
- This is the case for Omnicidal Maniac villains whose threat is considered universe-reaching, such as Darkseid or Thanos. Since their influence can threaten the entire fabric of existence, letting them get their way even once would be an unstoppable catastrophe upon life itself.
- Sonic the Hedgehog (Archie Comics) had this with Dr. Robotnik/Eggman as one good victory against Sonic meant that he can easily trample through the resistance with ease. A good idea of this was the Time Skip when Sonic was in space - without Sonic around to stop him, Eggman was able to regain all of his lost areas and then some.
- In Emily Carroll's collection of short stories Through the Woods, the final story "In Conclusion" features a version of Red Riding Hood (implied to be a semi-autobiographical of Carroll herself as a child.) The girl passes through the woods without incident to her grandmother's house, and as she's settling down to sleep she remarks that she knew the wolf wouldn't find her.
"Oh, but you must travel through those woods again and again..." said a shadow at the window. "...and you must be lucky to avoid the wolf every time...
But the wolf...the wolf only needs enough luck to find you ONCE. "
- A one-shot villain created by a decent soul being yanked into hell and tortured into serving a demonic master after losing to Superman and being taken back to hell when questioned about his failure explicitly states that it's but the start of things and that his success is certain because he only needs to win once while Superman must win every time.
- Brainiac invokes this in one story by saying "I only need to win once!".
- The Plague of the Antibiotic Man: Amalak mocks Superman's choice to leave him alive after defeating him by stating Superman is giving him more chances to kill him, and he only needs one successful try.
- The Superman Adventures: As Lex Luthor points out in Issue #27, those trying to kill Superman only need to be lucky once.
- An issue of Nintendo Comics System focusing on The Legend of Zelda segment has Zelda say this. Link beats Ganon over and over, but if Ganon wins once and gets the other Triforce, he'll be unbeatable. They go on a quest for a magic flute she'll use to take the Triforce to another kingdom where Ganon will never find it, but she'll never see Link or Hyrule again. She changes her mind and decides to stick around at the end.
- In Power Girl fanfic A Force of Four, Wonder Woman mocks Badra's "one-time villain" status. As striking Wonder Woman, Badra reminds her that one successful attempt is everything she needs.
"A 'great one-shot wonder,' am I?" asked Badra, slapping Diana again. And again. And again. "Perhaps I won't need more than two shots to achieve my objectives. Will I, Diana? Will I?"
- Discussed in Crush. While Loki insists this trope is true, Tony claims that his side can make all kinds of little mistakes and that they wouldn't be making big mistakes anytime soon.
Loki: 'Anytime soon'.
- Webwork: Jade justifies her losing streak in the Essence hunt to Tarakudo by pointing out that each loss has been narrower than the last. Sooner or later, they'll succeed in gaining at least one General on their side, and that one victory is all they need to tip the scales in their favor.
- Discussed in Chapter 4 of What the Cat Dragged In. Hawkmoth doesn't lose anything but time when his akumas are defeated, and the glamour seems to make it impossible to track where akumas appear from or disappear to. In short, Hawkmoth can keep trying as many times as he wants, until eventually one of his akumas gets the Miraculouses.
- In Dance with the Demons, Ra's Al Ghul points out that, should he want Batman killed, he would simply send his sleeping terrorist cells against Batman one after another. Eventually, one of them would succeed.
Ra's Al Ghul: "Why would I want you to come after me? Were I to desire your life, I would simply activate a group of my men from anywhere in the globe, and send them against you. You might triumph over one or many, but eventually one would kill you. This is a certainty, Detective."
- Defied in Friends of Family. Mayday Parker explicitly references this trope in her opening narration, observing that Peter kept saving the city, over and over again, and no matter how many times he got knocked down, he always got back up... until his Rogues Gallery didn't, because fighting a superhero takes its toll on you eventually.
Mary-Jane: The thing is... he became Spider-Man because people like Norman and Otto and Eddie were running around raising havoc. People who normal people couldn't deal with. And one day, they just stopped showing up. When he went on reconnaissance, he found Norman in a wheelchair, Otto with an oxygen tank, and Eddie in the streets.
- In Epic (2013) it's not made explicit, but it's pretty clear if Mandrake stops a new queen from being crowned, the forest wouldn't be able to come back from him rotting it.
- Demon Knight: Before there was light, there was darkness, populated by demonic forces of evil. All God could do to keep them at bay and allow the Genesis was taking their seven keys and scattering them throughout the universe. The demons have retrieved all the keys minus one, which is protected by the titular Demon Knight of Earth. If the Collector gets his hands on it, the entire universe will fall back into a chaos of horrors.
- In The Fifth Element, the personification of evil springs up every 5000 years. The titular element has to be used in conjunction with the four element stones to wipe it out, but it keeps coming back. If evil gets the four stones, however, it can wipe out all life in the universe. No recovering from that.
- In The Cabin in the Woods, the Ancient Ones are kept asleep by giving them sacrifices. The sacrifices have to happen every year (there are numerous backups, and at least one has to succeed), but missing the deadline means the Ancient Ones wake up and the world is screwed. Played with in this case, as evil need only win once to prevent oblivion from winning, but also needs to win every year to prevent oblivion from winning once.
- Deconstructed in The Avengers (2012). In a confrontation with Loki before the final battle, Tony explains just how bad of a position Loki would be in even if he were to win:
Tony: "There is no version of this where you come out on top. Maybe your army comes, and maybe it's too much for us, but it's all on you. 'Cause if we can't protect the Earth, you can be damn well sure we'll avenge it.
- In Star Wars, there is a reason the Empire always loses when it brings forth the Death Star and its evolutions in big fights, while it can win other fights with just Star Destroyers and Walkers. These superweapons are too destructive and can eliminate the heroes too quickly if they ever win. Which is why they don't, as if they do so, the heroes can't recover.
- In An Outcast in Another World, if the Blight reaches a Locus of Power, it turns the surrounding area into a land that is uninhabitable and toxic. This is permanent, irreversible, and spread many miles out from the point of origin. Considering that the entire western edge of the continent was consigned to this fate and is now called The Deadlands, every failure to prevent this from happening is a loss that can never be undone.
- In Discworld Vimes thinks this about the repeated assassination attempts he suffers. However, in the end, the Assassin's Guild declines to accept more commissions on him. One reason is that his role in the management of the city has grown vital enough that they don't want the disruption removing him would cause. The other is that their repeated failures were just getting embarrassing, and assassins value their own lives highly.
- The Last Hero Cohen the Barbarian says it doesn't matter if he fails to kill the Discworld Gods, it just matters he tries because "Next time someone'll try harder".
- In A Night in the Lonesome October by Roger Zelazny, the villains are trying to perform a ritual that will open a gateway into the world for a collection of Lovecraftian Eldritch Abominations. Every previous attempt to perform the Opening has been defeated, but as long as the ritual exists there will always be someone sooner or later willing to try it and it only needs to succeed once.
- In The Wheel of Time, this a major concern due to Eternal Recurrence — when the heroes win, the Dark One stays imprisoned, but if the Dark One breaks free, he'll destroy the Pattern and remake creation in his own image. There are several in-universe theories why it hasn't happened:
- Some Aes Sedai believe that The Multiverse keeps him trapped — paradoxically, he only needs to win once to break free, but can't truly break free as long as even one reality stands unbeaten. There are hints in the story that he has won before, only to find his efforts rendered futile as the Reset Button was pressed.
- The Chosen One comes to believe that the Dark One is doomed to fail because he's a static, sterile, utterly selfish force of evil that can never learn from his mistakes or understand how humans choose to stand against him for the good of the world.
- This is also central to Ishamael's view of life. A former philosopher, he became savvy both to the endless repetitions of the Wheel and the fact that Evil Only Has To Win Once, and decided that not only was saving existence impossible (since the Dark One has an eternity to get it right), but since the cycle only repeated variations of the same events over and over again with no hope of true change, existence wasn't worth saving.
- Roland of The Dark Tower is seeking the aforementioned Tower to save it. He's also stuck in a Stable Time Loop and must repeat his adventure over and over, meaning he has to save the Tower numerous times. In comparison, the Crimson King only needs to win once to destroy reality and plunge all its denizens into the primordial chaos.
- If it was a stable time loop, that wouldn't be a problem, since everything plays out the same way every time. But there may be slight changes every time it's repeated (Horn of Eld), so the outcome really is unsure.
- The implication is that it cuts both ways. Roland saves the Tower, but he's done so many terrible things to reach it that by the time he does, he's unworthy of it. However, through the love of his friends, he's redeemed himself just enough to earn a second chance. Presumably if he ever manages to make it to the Tower without compromising his humanity in the first place, he'll be worthy enough to ascend to the top and fix Creation such that it never needs saving in the first place. Evil Only Has To Win Once... but GOOD also only has to win, really decisively WIN, once as well.
- The Cthulhu Mythos is full of Eldritch Abominations lurking in other dimensions, many of whom could destroy the world (or the entire physical universe) if they felt like it. So if some insane cultists ever succeed in waking one of them up, it's all over red rover.
- The Lord of the Rings averts the trope in the specific context of its Big Bad, but follows it concerning evil in general. As Gandalf explains, if Sauron wins his victory will be so complete that none can foresee his fall while the world lasts, but if he falls, he will fall so low that none can foresee him rising ever again. However, As Long as There Is Evil (which there will always be since it was woven into the fabric of creation itself by Morgoth), "the shadow will ever take another shape and grow again." To highlight this point, Sauron is the second shadowy, all-powerful force to attempt to dominate and envelop all creation; the first being Morgoth, Sauron's former boss.
- In the Doctor Who Past Doctor Adventures novel Festival of Death, the Doctor and his allies prevent an Eldritch Abomination from eating the universe. So far, just another day in the office for the Doctor. But there are several time loops involved, so there's a sense in which the adventure is happening over and over again forever — and if the Doctor and his allies slip up even once, it's goodbye universe.
"Yes," said the baby, opening its eyes. "The Doctor succeeded. This time."
- Averted in Villains by Necessity itself an inversion of the Standard Fantasy Setting. The forces of Good did win the ultimate battle two centuries ago and have been turning the world into a Sugar Bowl ever since. A druid convinces some of the few remaining evil people in the world to restore the Balance Between Good and Evil by releasing the Sealed Evil in a Can.
- In the Tom Clancy novelnote Patriot Games, the ULA terrorist Sean Miller notes that anti-terrorist forces have to be lucky every time, while terrorists only have to do so once, in a nod to a similar comment made in the aftermath of the Real Life Brighton hotel bombing.
- In the Chronicles of Thomas Covenant, Big Bad Lord Foul is essentially immortal- he can be imprisoned or reduced to near impotence, but "Despite can never die" and he'll always return to power. On the other hand, Foul's own goal is to destroy the Arch of Time and, by extension, the physical world (because he's trapped there, and he wants to escape back into the wider universe and get back at the Creator, his Good Counterpart who trapped him in the first place) some which, needless to say, only needs to be done once. Any hero who successfully defeats Foul, though, has to live with the knowledge that he'll be back a few millennia down the line.
- In The Dresden Files:
- Harry discusses and dismisses the idea when talking with the book's Big Bad Nicodemus. Sure Nicodemus and his group of humans possessed by Fallen Angels could win this battle, gain access to a powerful magical weapon, and cause the end of the world, but does he really think Heaven won't fight back tooth and nail within their bounds? That three new Knights of the Cross, men or women who take up a Sword with a Nail from the Cross Jesus was Crucified on in the hilt, won't rise up a previous Knight is killed or unable to fight? That good people in general won't stop fighting? Harry says such an idea is foolish and likely a source of Nicodemus' deepest fears because his plans have been foiled countless times by such good people being in the right place at the right time.
- On a scale larger than Nicodemus, The Adversary is a group of Outsiders that want to unmake reality and are only prevented from doing so by Queen Mab and those who guard the edge of reality.
- Inverted in the Lensman series. The Arisians are completely indestructible against any existing force, so if Boskone's current agent is able to defeat Civilization, them's the breaks; the Arisians are perfectly capable of raising a new Civilization, new Lensmen, and a new Super Breeding Program until they finally produce the weapon that can take down the Eddorians for good.
- Uprooted has this in regards to the Wood. In accordance with its planty nature, it can spread dozens of malicious "seeds" (i.e. infectious wolves, evil magic tomes, actual pollen), all at little cost to itself. The people of Polnya have to expend a lot of energy to stamp out just one that takes hold, and if it ends up combining with another, things get ugly fast.
- A key point of Daniil Andreyev's Роза Мира (Rose of the World): If a world-wide dictatorship were to occur, it is likely that the ruler(s) would be unwilling to let go of their power. Ever. And with (eventually) no other states to oppose the sole superstate, only a Civil War would offer any hope of change (and not much hope as it'd likely be a Revolving Door Revolution).note
- In A Practical Guide to Evil, the Black Knight isn't out for destroying the world, but for the sheer shock value of Evil winning: he mentions that if he can lead Evil to victory even once, he'll have broken the divine law that Good always wins and forever afterwards, every hero will have to live with the fear of defeat.
- Bazil Broketail: Lessis says this in the first book, warning officials of Marneri that the Enemy need only get one decisive victory to destroy them all, while they must stop every major attack.
- In Buffy the Vampire Slayer, Spike asks Buffy how many vampires, demons, etc she thinks she's killed.
Buffy: Not enough.Spike: (nods) And we just keep coming. But you can kill a hundred, a thousand, a thousand thousand and the enemies of Hell besides and all we need is for one of us- just one- sooner or later to have the thing we're all hoping for.Buffy: And that would be what?(Spike leans in close and whispers in her ear.)Spike: One... good... day.
- In the context of the episode, Buffy is worried about being killed in the line of duty and wants to find out how Spike managed to kill two Slayers over the years. Spike explains that there is no big secret: partially by luck, he just managed to have a good day and the other Slayers had a bad one. Before Buffy, no Slayer has ever lived past 25 years old. It's a dangerous job and they just have a high turnover rate due to simple attrition. The adult son of one of the Slayers he killed later even confronts him about it, and Spike points out that if he didn't kill his mother, some other vampire eventually would have - few Slayers ever choose to have children because they know how dangerous their lives are, his mother knew when she had him that she was in a high-risk lifestyle which would probably leave him an orphan at a young age, but she chose that anyway. The Slayer's son actually accepts this as a good explanation and doesn't feel a great need to seek revenge against Spike afterwards.
- All that said, from a larger perspective the show averts this trope. Whenever one Slayer dies, another one is immediately called, meaning that it's as impossible for evil to triumph permanently as it is for good. The spinoff Angel also expanded the universe to show that the Slayer is only one of many champions throughout the world standing against the forces of darkness. The series finale even had Buffy instruct Angel to prepare a second line of defense in case the seasonal villain beat her, meaning that even if it had won that battle, it would still have been nowhere close to winning the war.
- Angel's main villains, the demonic law firm Wolfram & Hart and their allies, play with it. As far as they're concerned evil has already won and Omnicidal Maniac villains who tend to feature on Buffy are as much a threat to them as to the good side. As to their specific interests and clients... eh, you win some, you lose some. In fact, the most apocalyptic threat the heroes faced was from a "good" quasi-deity.
- Inverted in an episode of Monk, where the titular character is talking to a group of children about what he does as a detective. He says that he has made some mistakes as a detective and that good guys and bad guys can both make mistakes, but a bad guy only has to make one mistake for the good guys to find him and arrest him.
- Inverted in Narcos - In the fourth episode Steve says that Escobar needs to be lucky every time they come for him, while the DEA only needs to be lucky once.
- Coupled with Not-So-Harmless Villain and a dash of Fridge Horror in any given season of Power Rangers. As ridiculous looking as some of the monsters can be, they can still wreak massive amounts of destruction and the Megazord is the only thing that can stop them. If the Rangers lose, the villains just got rid of their only obstacle to world domination.
- Kamen Rider Wizard had this, seemingly the result of the writers putting themselves in a corner. Short version: There are special people with magical potential (Gates), but if they cross the Despair Event Horizon, they die and get replaced by a monster called a Phantom. The title character is a Gate who fought back from the edge of despair, unlocked his latent magical powers, and uses them to protect other Gates from the Phantoms. The problem is that if the Phantoms succeed even once, then Wizard will fall into despair over his failure and become a Phantom. This kills a lot of the show's dramatic tension and makes it so that the villains never succeed at any their goals except for the Big Bad and The Starscream, both of whom had hidden agendas besides creating more Phantoms.
- Explicitly referenced in the lyrics to Ookla the Mok's song "Suprema Lex" on the Vs. Evil album. The song is a prolonged monologue from Lex Luthor delivered to Superman and the title is a clever play on the Latin maxim "salus populi suprema lex esto" meaning "the good of the people/society is the highest law". The song includes the lyrics: "And it doesn't matter where, it doesn't matter when / And though I may lose again and again / Remember there's just one thing you've got to keep in mind / I only need to win one time."
- Christianity inverts this: since God is omnipotent, He only has to beat Satan once for the Devil to be permanently unable to harm anyone ever again, and it’s implied that the only reason He hasn’t done so already is to give humans time to repent. Taken even further because Satan can never win at all; it is certain he will lose at Armageddon.
- This is why the gods of Egyptian Mythology demand worship from mortals—they need it so that Ra is strong enough to stop Apophis from destroying everything. Even the gods would die if Apophis won, so even one failure is not an option. This happens every night.
- Doom: The Board Game by Fantasy Flight Games features a campaign mode where the Space Marine players have to win all five scenarios while the Invader player only needs to win one in order to win the whole campaign. The Marines get to keep their equipment between games, though.
- Battletech kinda inverts this with the proposal of Victor Steiner-Davion (representing the "good" Inner Sphere) to the "evil" Clans; the latter being hell-bent on conquering Earth. He challenges them to a refusal test with two possible outcomes: Either the Spherians win and the Clans have to leave them alone for good, or the Clanners win and thus have earned the right to wage perpetual warfare against the Inner Sphere until they've completed their conquest (or are vanquished for good themselves) - because permanent war is what their whole society is tailored to.
- Eberron: The demon Overlords are sealed around the world, and the keys to their unsealing hidden in the Draconic Prophecy. There is always an opportunity for them to be unsealed—even if every avenue of escape is countered, the Prophecy is a living thing, and new potential escapes will be created. Eventually, one will get out. However, if one of them is unsealed, the opposite is also true: There will always be a way to re-seal them. In fact, in the backstory, Thrane was all but destroyed a few centuries ago when an Overlord escaped. The campaign and sacrifice to re-seal it created the Church of the Silver Flame, one of the greatest forces opposing supernatural evil in the world.
- In The Lord of the Rings Risk game, this trope is the essential mechanic to the Good vs Evil gameplay mode. The One Ring moves along its path towards Mt Doom at the end of each turn. If an Evil player controls the territory it was in, they get a chance to find/claim it by rolling a 12 (or lower if they have other factors in play). Good wins if the game lasts long enough for the Ring to reach the end of the path, but Evil wins if they can even once find/claim the ring at any point during the game. Ironically, this means the game balance is very much the reverse of the situation in the books: the two Evil players must work together and coordinate their plans to have any chance of actually winning before the game ends, while the two Good players are fairly free to bicker and backstab each other for personal advantage without significantly hurting their odds of being the winning team.
- Warhammer 40,000: Chaos only has to win once. The Inquisition may be working overtime to root out cults and heretics, along with the Grey Knights taking down any Daemons that may pop up, but the moment Chaos wins, it's over for that planet. The planet will be terraformed into a Daemon World, where reality ceases to exist, and most importantly, makes it virtually immune against Exterminatus, ensuring its denizens will be trapped in perpetual hell with no hope of escaping. It's telling that when Chaos is close to winning, the best course of action is to commit the planet to Exterminatus, as it denies Chaos of victory and spares the inhabitants from eternal torment.
- In a sense, this trope is inverted with any game that has a extra life system. In this case, the player really only has to win the one time to beat the game. The antagonists have to keep winning in order to stop the player from doing so.
- Taken to its logical conclusion in Undertale: Given enough determination and in-universe Save Scumming, the protagonist can never truly be defeated. If you take the Villain Protagonist route, the only hope of the heroes you fight is that you get bored or frustrated and quit. And if you complete this route just once, your game will be forever ruined; even doing the pacifist route afterwards still results in the Fallen Child escaping the Underground and being able to wreak havoc on humanity. You can go so far as to alter or even delete the files on your computer, which will in fact allow you to earn the Pacifist ending again, but even then the game still knows you did that and will call you out on it. There's no escaping the consequences of allowing the Fallen Child a single victory — after all, creating the most horrific, cruel ending scenario possible was entirely your decision.
- Non-plot variant in Unreal Tournament: in Assault mode's rules. The match consists of two rounds, one defense and one offense; if the attackers in the first round win, they swap roles with the defenders and the new attackers must win faster. Example: your team starts with offense. If you lose the offense round, you instantly lose the match. If you win the offense round but lose the defense one, you lose the match as well. Under the same rules, if you were to start with defense you could win the match either by winning defense OR losing defense but beating the other team's time in offense... but if you play against the AI, you always start with offense and therefore you can't afford to lose even once. This can be particularly frustrating since the bots on your team are severely handicapped in Assault mode.
- The Soul Series. So far, the Soul Edge (the evil sword) has been shattered or destroyed at least three times (Soul Edge/Blade, Soul Calibur 1, Soul Calibur 2), twice by the Soul Calibur (the "good" sword). What happens each time? The sword just breaks into pieces (each one every bit as evil as the whole sword) and eventually reforms itself, stronger than before. Now, what happens in every ending where the Soul Edge wins instead? The world gets hosed, that's what. Even worse, in SCIV, we learn that the Calibur is actually just as evil, but with a penchant for Order rather than Chaos. This was amplified in the 4th game, where several endings had the "good" sword freezing all life in crystals in order to prevent humanity from ever reforging Soul Edge.
- Mortal Kombat is mentioned in the trope description, but it's actually more of a funny variant of the trope rather than a completely straight example. By the time the events of the original game play out (after being Ret-Canon'd by the movie), not only has evil already won once but has been doing so for the past 500 years or so. The tournament that is being documented by the game is actually the tenth such tournament following a string of nine victories by current champion Goro. If the Earthrealm fighters fail to crown a champion of their own in this tournament, Shao Kahn and Outworld have free rein to invade and conquer Earthrealm. So in Mortal Kombat's case, it's "Evil Only Has To Win One More Time". A look into the series' backstory reveals that the entire tournament is actually rigged to keep anyone from uniting all of the Realms. The Elder Gods split the Realms to prevent the One Being from ever returning. Evil only has to win one more time... but the ones in charge won't let it win if they can help it.
- Castlevania operates on this principle, though so far it hasn't had to actually employ the trope. Every hundred years, Dracula's castle reappears, and whoever in the Belmont clan currently possesses the Vampire Killer whip has to storm the castle and slap Dracula back to the abyss. Should they fail... well, everyone's going to pay the price, but all Dracula has to do is wait another hundred years (a stone's throw in vampire time) and he gets to try all over again (until 1999 and a well-timed eclipse screwed him over for good). It's even more apparent in that Dracula is also resurrected several times outside of this hundred-year loop (Shaft controlling Richter Belmont five years after Rondo of Blood to resurrect Dracula in Symphony of the Night, the death and destruction caused by the World Wars bringing the castle back in Bloodlines and Portrait of Ruin, or the eponymous Order of Ecclesia utilizing glyphs to resurrect Dracula), but none of these obstruct the "fated" resurrections, which happen on their own regardless.
- Played straight in the ending of Baldur's Gate II: Shadows of Amn: the main character is facing moral challenges in Hell, with various choices each with two different possible outcomes, one is "good" and the other "evil", the latter representing a character following the nature of a spawn of the god of murder. Even a lawful good paladin that always made good deeds in the game and chooses the good choice in all trials but one, will instantly become evil, because for a single moment, he/she succumbed to Bhaal's taint.
- Possibly averted in the ending of Throne of Bhaal: a good character can choose to embrace the divine power of Bhaal, purified by its evil essence, and become a power of goodness in the planes. While this doesn't stop evil per se from existing, nor murder as the current god of murder Cyric is still in charge, it stops specifically the Bhaal's taint, which caused so much suffering and havoc during the game, from infesting the world once and for all.
- Inverted in the Mass Effect series, where the success of the Reapers' periodic genocidal "harvesting" of spacefaring civilizations is largely dependent on leaving no survivors who might warn future civilizations or try to interfere directly. True to form, things fell apart for them once a few surviving Protheans sabotaged the system intended to awaken the Reapers from hibernation and allow them to strike first with a surprise attack at the heart of galactic civilization. The weapon needed to defeat them was incrementally designed and improved over countless cycles (the Reapers thought they'd erased the design several times), and presumably only the original creators actually knew what the hell it did beyond being the superweapon the previous cycle almost completed.
- This is most evident in Mass Effect 3's "Refusal" Ending: Even if Shepard fails this cycle, the Reapers finally fall in the next one.
- In Final Fantasy, there are two ways to break the Stable Time Loop: for Garland to beat you in your first battle, or for you to kill Final Boss Chaos in your last battle. In the first case, evil wins, in the second case, you win. It's stated that the loop has gone the same way (Warriors of Light beating Garland then getting killed by Chaos) thousands of times.
- Final Fantasy XIV has a version of this where the Ascians have been behind each of the many Calamities that led to the Umbral Ages of Hydaelyn. Heavensward reveals that they do this to revive their god Zodiark, the antithesis to Hydaelyn, and they need 13 pieces. Granted, this means that they're not quite there yet - even by the time of the Seventh Umbral Calamity that ended the storyline of the game's original release, they're only about halfway through. It's also revealed that they even have some failures - the Void was created by the Ascians flooding a "shard" (a separate world that acts as a "reflection" of the world the game normally takes place in) in darkness, creating a haven for demonkind rather than properly destroying that shard, and the setting of Shadowbringers is on another shard that is on the cusp of a similar fate to a flood of light.
- It could be said that that "Evil Only Has to Win Once Each" - every Umbral Calamity that the Ascians induce causes a shard to be destroyed, ending every life upon it. So while the Source (the world the game mainly takes place in) can endure and survive the Calamities with enough effort, it's already way too late for seven of the thirteen shards. Shadowbringers reveals that there is a way around this via Time Travel - hells, the events of that expansion take place entirely because G'raha Tia went back in time to avert the Eighth Umbral Calamity - but Word of God has insisted that the world he came from has continued on in a proper Alternate Universe.
- And then, in the aftermath of Shadowbringers, evil really does only have to win once. Both evils, as it happens. First, Elidibus manages to wrest control of the Crystal Tower from G'raha, and gained access to his memories - including the Time Travel magic. The only thing stopping him from going back in time and making the Ascians' endeavours all the more successful than they've already been is the fact that he really wants to kill the Warrior of Light, right here, right now, which gives them the chance to kill him first. Then, once he's dealt with, Fandaniel goes full Omnicidal Maniac and means to bring about the Final Days, destroying every life not only on the Source but on every shard reflected from it, himself included. If the Scions don't manage to find the cause and avert it, then evil has won from beyond the grave.
- While Dark Souls runs on Grey-and-Grey Morality, this is invoked by the game's central conflict. In order to keep the First Flame alive, the followers of Gwyn must always keep the cycle of sacrifice going in order to continue the Age of Fire. However, all the followers of Kaathe and the Pygmy have to do is merely wait for the First Flame to die.
- Dark Souls II casts doubt on this. It would seem that both sides are locked into this as part of an Eternal Recurrence of Light and Dark. The First Flame did not go out completely regardless of your actions in the first game; if you didn't link the fire, then someone else did. It only takes one person to end the cycle, and only one person to start it again.
- Dark Souls III muddles the issue even further. All of the destruction wrought by the Cycle has been permanently screwing up the world with each cycle. The latest cycle may very well be the last one, and it's not clear whether a "good" ending is even possible anymore.
- Inverted in Star Wars Battlefront (2015), if you're playing Infiltration over Scarif or Battle Station on the Death Star. All it takes is one U-Wing to make it through Scarif's shielding, or one X-Wing to reach the end of the Death Star's trenches, and the rebels have won the round. The Empire has to shoot down everyone who tries.
- Team Fortress 2: In Mann versus Machine mode, only one bot has to make it past defenses with the bomb for the defenders to lose.
- Averted in The Legend of Zelda, because Ganondorf is much better at conquering things than he is at holding on to his conquests. He's won three times and been overthrown each time, despite having the deck stacked massively in his favor (being literally an immortal wizard, being highly intelligent and probably quite well-educated, and having the power of one of the gods of the setting and its Devil-counterpart as well):
- Ocarina of Time: He conquered Hyrule, dealt wholesale strategic destruction to its various populations (apart from his homeland, the Gerudos), and retired into his castle, leaving his minions to deal with the embittered remnants of the world's population. Link got the assistance of these scattered remnants and challenged Ganondorf in his castle. If Link wins in this fight, the timeline splits into the Child Timeline (where Link goes back in time, thwarts stage one, and leads to Twilight Princess) and the Adult Timeline (where Zelda rebuilds Hyrule after Link's departure, leading to Wind Waker below). If Link loses this fight (which means that evil has already won twice), it leads to the Downfall timeline, where said scattered remnants eventually managed to seal Ganondorf away from Hyrule anyways, leading to A Link to the Past and eventually Zelda I below.
- The Wind Waker: Centuries after being sealed away by the Sages after Link's victory, Ganon returned and swept away all opposition, forcing the goddesses to drown Hyrule under a new ocean in order to stop him. Ganondorf eventually broke out of his underwater prison and began rebuilding his forces, but Link got the assistance of the scattered descendants of Hyrule's original population, challenged Ganondorf in his castle, and defeated him before he could reconquer Hyrule's remnants.
- The original The Legend of Zelda: Link arrived in a burned-out wilderness, a Hyrule utterly devastated by Ganon (the usual name for Ganondorf in boar-demon form) and his minions: a miscellaneous army of ogres, adventurers, summoned monsters, tame dragons, wild centaurs, unquiet spirits, Giant Enemy Crabs, and animated suits of armor. But there were still a few survivors, hiding out in caves and mountain glens; Link got the assistance of the scattered remnants of the population, challenged Ganon in his mountain (which had been hollowed out and surfaced internally to where it distinctly resembled a castle), and defeated him.
- Ganon's got a little better at the game by the time of The Legend of Zelda: Breath of the Wild. Calamity Ganon destroyed Hyrule a century beforehand, killing Link in the process. It was sealed within Hyrule Castle but the seal is increasingly diminishing (by the time of the game it's very nearly broken) and if it ravages the land again, it's The End of the World as We Know It. The people have been unable to do anything about it and Zelda's prayers are the only thing keeping Calamity Ganon even remotely at bay. Link's journey in Breath of the Wild is viewed as the final opportunity to put an end to the blight.
- Bowser in Super Mario Bros. fits this trope quite well; and there's an interesting difference here between Nintendo's two flagship franchises, Super Mario Brothers and The Legend of Zelda. Bowser has none of Ganondorf's patience or dark charisma, none of his gift for intrigue, little of his impromptu gallantry, and not a whole lot of his personal courage; but he's willing and able to install garrisons, collect taxes, spare civilian populations, and generally rule. Ganondorf likes winning, Bowser likes having won; and so Bowser, although less dangerous and less intimidating, is the one who can make his conquests stick. Mario can never risk defeat against him — not even in a go-kart race.
- Subverted in Knights of the Old Republic. Carth certainly thinks this is true, but Jolee is less concerned, believing that things would bounce back to normal even if evil did win - though it wouldn't be until after a few decades, or centuries, of tyranny, and he'd rather not wait that long.
- Inverted in the Gardens & Graveyards Mode of Plants vs Zombies: Garden Warfare. The Zombies are in a Timed Mission to take down each of the Plants' strongholds; if the Plants manage to fend them off long enough for the time to run out even once, the game automatically ends with their victory.
- Fire Emblem: Awakening establishes that the Fell Dragon Grima returns to destroy humanity once every 1000 years, meaning that, statistically speaking, humanity is doomed because Grima only has to succeed once whereas humanity has to defeat Grima an effectively infinite number of times. The last act of the game gives the player, and by extension their Avatar, the choice to let Chrom strike Grima down, only guaranteeing another 1000 years of survival, or deal the final blow personally and sacrifice themself to kill Grima permanently.
- One of the possible endings of Devil Survivor 2's Triangulum Arc. After learning that destroying Canopus will just prompt another Administrator to step in and try to destroy the world, your party can decide to regress the world anyway and fight the new guy, over and over and over until, eventually, they run out of Administrators. It's made quite clear that if ever your party loses, the world will be destroyed for good and the whole thing will be for nothing.
- In Samurai Shodown II, by the time you reach Mizuki Rashojin, she's created all kinds of havoc worldwide, killed Amakusa, completely subjugated Ambrosia (the very being who turned her evil in the first place), and opened an extremely scary-looking gateway. Defeat her or the whole world literally goes to Hell.
- In Nefarious, this is nearly said word for word in the narration for the normal ending where Crow indeed wins and takes over the world.
- Averted and played with in Nexus Clash. The Evil Elder Powers have won the cycle (and the right to be the shaper of the next world) many times, but since it's an Eternal Recurrence they have also lost many times. What's more, the cause of a new cycle is the end of the world or human civilization on it. Thus while all the Powers have flaws that cause their worlds to fall apart eventually, the worlds shaped by the Evil Powers are self-destructive, short-lived hellholes that quickly crumble and leave creation up for grabs by better and saner Powers.
- World of Warcraft: This is the modus operandi of the Old God N'Zoth. At any given time, he has dozens of schemes to corrupt or destroy Azeroth underway (Most notably, he is responsible for Deathwing, Azshara, and the Infinite Dragonflight). Many of them have been thwarted by the heroes, but he's always got another one and he only needs one of them to eventually succeed for him to win.
- In the campaign game mode of Fantasy General, you play as one of the Council of Five's generals who are trying to liberate the world from the evil Shadowlord. The manual tells you that the Shadowlord is so powerful that you cannot afford any setbacks or delays — and indeed, losing only a single battle means losing the entire campaign.
- Averted in Evil Genius 2: though the events of the first game are stated in-universe to have happened- an Evil Genius successfully took over the world using the ID Eliminator device- by the time of the sequel, said Genius has apparently been toppled from their rule, and the world has more or less gone back to normal, allowing the Geniuses of the second game to rise and try for the throne.
- This aversion is actually the reason behind Emma's rise to Evil Genius status- she was a Spymaster for the Forces of Justice during the first game. Emma spent her entire life defeating Evil Geniuses and stopping them from taking over the world, only for the world to not learn its lesson and constantly go right back to the same circumstances that allowed megalomaniacal masterminds to take it over. This led Emma to become disillusioned with the Forces of Justice, leading to her current villainous career.
- RWBY has elements of this. The antagonist, Salem, is a witch with terrifying magical power and control over The Grimm, but what's more is that she has Complete Immortality, having been Barred from the Afterlife by both of the two gods who originally created the world and humanity. Learning this nearly drives half of the protagonists to the Despair Event Horizon, as they can spend their entire lives trying to keep Salem from getting her hands on the magical artifacts she needs to destroy the world, but she has all eternity to keep trying until she succeeds, and when she does it will render everything they've ever done or sacrificed moot.
- Poked fun at in Bug Martini, where the author points out that while 'evil only has to win once,' evil still has to get off its duff and make things happen, so it's really more of a fair fight than this trope usually implies.
- The world is in for any variety of apocalypses if the SCP Foundation fails to contain some threats. e.g. SCP-231-7 only has to give birth once.
- Dream: Evil only has to win once from Dream's point of view. If Dream dies once, his opponents win automatically unless Dream has killed the Ender Dragon before then. The hunters are not under that stipulation, however—they can die however many times they want and continue the fight, their only losing condition is Dream killing the Ender Dragon.
- Man Of Action's Generator Rex joins the party with the introduction of the meta-nanites, special nanites which can bestow the power over things like matter, antimatter and the like, if Van Kleiss, the Consortium (Providence's higher-ups who intend to use them and become gods) or Black Knight who intends to acquire their power for herself, gets their hands on them it's game over. It turns out that Evil never had a chance in the first place. The Meta-nanites had been programmed by Cesar and his parents in such a way that only Rex could use their full power. That is the only reason Cesar cooperated with Black Knight to gather the Meta-nanites in the first place — he had been planning to give that power to Rex all along. Too bad he never told Rex that.
- This is the underlying premise of Beast Machines. The Maximals finally come out on top in the finale of its predecessor, Beast Wars, but as they drag him back home to Cybertron, Megatron has "one good day" and exits the time-and-space traveling journey home, enabling him to conquer the planet before the Maximals return, wiping out their victory in a matter of seconds.
- In The Legend of Korra, this is the case with Vaatu. If he triumphs, good will eventually reemerge, but it will take 10,000 years, during which he will be left free to ravage the world. He just has to win one battle on the right day.
- Skips from Regular Show has to repeatedly take down Klorgbane every 157 years. He only has to beat Skips once to kill his brothers (as shown with Archibald being easily killed).
- This is why the Multiverse is at stake in Penn Zero: Part-Time Hero.
- Implied if not outright stated in the My Little Pony: Friendship Is Magic fifth season finale, the Cutie Re-Mark. Each "Bad Future" visited has a different evil overlord. While the others may have been somehow defeated as they were in canon, it only takes one winning because of the different timeline to turn Equestria into a complete Crapsack World.
- In Miraculous Ladybug, the heroes have to stop Hawk Moth's villains from getting their Miraculouses. If Hawk Moth succeeds only once, he can make his wish and that's the ballgame.
- Batman Beyond: Terry is getting tired of balancing his normal life and superhero life and tries to tell Bruce he wants a break for at least one day. The latter isn't having any of it because Gotham will always need Batman.
Terry: One night's not gonna make any difference!
Bruce: [grabs him by his shirt] One night always makes the difference!
- Initially subverted in The Dreamstone. Odd early occasions had Zordrak temporarily get his hands on the stone and successfully send nightmares to the Sleeping World which, while a horrific experience, had no long-term consequences and served merely as a rare petty victory for the bad guys. Later episodes had Zordrak concoct new, more devastating apparitions for the stone; to corrupt its powers and use it to make him unassailable "Lord of the Universe", making each time his minions stole it a Race Against the Clock.