Oddly Common Rarity

""I knew this 'I'm the only one! I'm the only one!' thing was just an attention-getter.""

- Xander on finding out there's more than one Slayer.

Our protagonist is one of a kind. Maybe he's mastered a kind of magic that only one person every zillion years is born with, or perhaps he's been given possession of a unique amulet that renders him The Chosen One. Everyone around him gasps at his inherent specialness and comments on how rare it is to meet someone with such a privileged destiny. Certainly, they've never met anyone as powerful as him before.

Yet, somehow, everywhere the reader goes in the story, they keep tripping over characters with the same, or similar, assets and abilities that the hero has. That dratted trinket seems to have been made on a production line. So it turns out the hero's not alone -- not so much "There Is Another" as "half the world's population are pretty much in the same boat, but we're following this guy, so he's special."

This is a particular kind of Fridge Logic, and once the audience notices that everyone and their dog have this "one-of-a-kind" attribute it can be jarring.

Sometimes the author will realise this is happening and try to justify or Hand Wave it. Success varies. The most common explanation is that the hero's power draws them toward people with similar power, making them a selective Weirdness Magnet. Another approach is when the author shows that this small group of people always stick together, forming institutions and guilds to protect themselves against the majority of society. In these cases, consistency is key to maintaining a Willing Suspension of Disbelief. Sometimes, the writer never addresses why this unique power is so widespread. Masquerade may also make odd things appear much less common than they are, even if they are not its main subject but related to it.

It's not exactly a hanging offense. It's easy to see why it happens. Presented with choices, a single character can only pick one option. Even if the plot itself alters his attitude via Character Development, the fact stands that he's already made his choice. Other characters with similar attributes show up to illustrate the road not taken: What if The Hero had denied his call to adventure? What happens when someone with psychological issues becomes The Chosen One? What if the hero's parents had lived? You get the picture. These extra characters are a contrast with the protagonist's own story, either highlighting his nobility or showing him up and pointing out where he went wrong.

The same thing can happen with whole scenarios and sometimes entire plotlines. We're told that something is a "freak event," a one-in-a-billion situation, only to have it happen twelve times in the run of the series. This is slightly harder to justify, unless Generation Xerox turns up to claim its right to retell the same story.

See also There Is Another...but keep an eye on it to ensure that it is just one other, or it can become an Oddly Common Rarity instead.

Compare with The Chosen Many where there is an overt, organsied and often numerous band of Chosen Ones.

Biologically, there is a specific reason for this to occur. It's called the Founder's Effect. When a population moves to a new area and is only capable of creating children with the members of its own population, traits common among the population will be passed down with higher frequency: even if the original trait is overall extremely rare.

Anime and Manga

 * In Ranma ½, the Curse of Jusenkyo is said to be an obscure mystery, such that "no one knows the true horror". But during the manga series no less than nine such victims show up, and two entire civilizations are introduced that owe their existence to the Curse. Not to mention "Jusenkyo Mail Order Products", a company which sells specialized magical bathing supplies specifically targeting the Jusenkyo Curse Victim demographic. Okay, seven individuals might count as rare, but when there's a mail order company that deals exclusively with them, that's not a rarity, that's a subculture.
 * Most of those victims were connected to each other (Ranma and Genma were cursed in the same trip, Ryoga was cursed following them there) or lived near it (Shampoo, Mousse, Pantyhose Taro, Herb).
 * One Piece does this with the Fruits of the Devil. They're said to be extremely rare, and the fact that only four Devil Fruit users appear in the East Blue portion of the story would bear this out. But once the crew enters the Grand Line, every single major antagonist possesses a Devil Fruit power. One villain specifically stated they were more common on the Grand Line. One set of antagonists were an organization whose members were recruited BECAUSE of their abilities. Even so, the fruit is supposed to be rare, yet we've seen no less than 30-40 of them in the course of the story.
 * There's also the a special kind of haki (what would be Ki in other series) that only one in a million people have...Yet, we've met 6 different characters who have it, with an implied 7th. It is shown that people who have tend to be leaders, but it still seems odd.
 * An aversion appears, though, with the rare swords that Tashigi is very interested in. Zoro had three of them for awhile until a Marine rusted one away, and Tashigi has one herself. The only other person with another sword of this rarity is Hawkeye Mihawk.
 * ''It's a Super Saiyan Bargain Sale!" Arguably justified via Superpowerful Genetics -- all the half-breed Saiyans are descended from Goku and Vegeta, the most powerful examples of the species. It was also stated that the Saiyans where getting stronger which is why Freeza blew up the planet.
 * Parodied by Toriyama himself in Neko Makin Z where Z goes Super Neko Majin, after seeing Onio go Super Saiyan.
 * Naruto: The running joke is that any character with a covered eye has Sharingan (or more rarely, a Byakugan), which manage to show up quite a lot despite the fact that most of the people who could have it are supposed to be dead.
 * And the Rinnegan, also. Black Friday sale off, probably,.
 * This is in general a really big thing in Naruto, where things are originally introduced as extremely uncommon and then end up pretty normal. For example, the Rasengan is first introduced as a huge no-one-can-master-this big deal, and then we find out that
 * Its not a no-one-can-master-this deal. They were all just surprised the the Idiot Hero Naruto mastered it in a few days, instead of a few years like its supposed to take. Its also still rare since only can still use it.
 * Bleach: Also extremely big for doing this in a lot of areas. An example would be Bankai, which is said to be extremely complicated and difficult to attain, as well as being one of the main and most major requirements to be a captain. As it turns out,
 * In Busou Renkin, there are only 100 kakugane in the entire world. For some reason, 25 of them, one quarter, are in the hands of the Japanese. Considering this is supposed to be a worldwide organization fighting baddies scattered throughout the world, it makes you wonder if either there are more or if the rest of the world is just understaffed. Although, there appears to be kakugane that the organization did not account for, so it may be bigger than they thought.

Comic Books

 * In the various X-Men books, mutants are supposed to be incredibly rare - and at first they were - but by the time Grant Morrison took over writing the book, there were enough of them to populate an entire country, underground communities in (at least) America, England, and China, and their own "ethnic" neighborhood in New York. After a few massacres and a global event that reduced the canonical number of "known" mutants to 198 and made it literally impossible for new mutants to be born, writers still introduced new mutants on a regular basis - they were just ones that had always been around without anyone noticing instead of people who'd recently gotten powers.
 * Adamantium is an incredly rare and difficult to work with substance in the Marvel Universe. Wolverine's origin is virtually defined by the conjunction of his regeneration power, adamantium, and deadly combat training. Naturally, several of his enemies have basically those same traits.
 * Everyone knows that Superman is the last Kryptonian ... unless you count his cousin, various clones, a few prisoners in the Phantom Zone, and an entire city shrunken down by Brainiac. And, Great Scott!, Kryptonite Is Everywhere. Every now and then someone will try to work out some tortured rationale to allow him to still officially be "the last son of Krypton" - anything from pointing out that "last son" doesn't preclude other female Kryptonians to claiming that all other living Kryptonians were actually born off-planet to pointing out that, since the planet blew up shortly after his birth, he was the last born son of Krypton. Don't forget Daxamites, Daxam is a planet inhabited by Kryptonians who left Krypton. Most if not all have only conceived with other Daxamites making them full blooded Kryptonians who happen to live under a red sun.
 * At one point, the Green Lantern Corps' "policy" was 2 members per space sector. Somehow, Earth manages to have 3-4 members at the same time. It's usually explained that while two patrol Earth's sector, the others are special ops stationed on Oa.
 * Mostly averted throughout the Silver Age (and irrelevant in the Golden Age, when there was no Corps). When the Corps basically collapsed on itself post-Millenium, Earth's Green Lantern Retirement Community marketing campaign apparently went into overdrive. Prior to that, it might have been hard to keep track of who was Green Lantern this week, but for the most part they were only one at a time, with an additional one sort of in standby/reserve status. (Alan Scott doesn't count; he was from the Earth-2 universe, and never a member of the Corps in the first place.)

Literature

 * In Harry Potter, Hermione says that there were only seven Animagi registered with the Ministry in the entire century. It is supposedly extremely difficult magic to master. Yet three out of four Marauders (excluding ) and are unregistered Animagi. That's a 54% increase over the official count, and those are all in the same generation and they're just the ones the trio happens to find out about. It looks like the rarity is people giving up their disguise to the Ministry, rather than learning the magic in the first place.
 * And no wonder, when you think about it. As touched on in The Tales of Beedle the Bard, being an Animagi has enormous potential for abuse, so it makes sense to think quite a few people would try to master it for their own ends and, if those ends were somewhat less than legal, not tell the Ministry about it.
 * The Dragonriders of Pern series does this with both powers and storylines:
 * We're told the ability to hear all dragons, other than your own, telepathically linked dragon, is extremely rare, but in the story's "main" time period alone (Masterharper of Pern to The Skies Of Pern chronologically) we have Lessa, Brekke, Aramina and arguably Robinton. This power affects its users differently. Lessa employs it effectively and doesn't think much of it. It becomes a lifeline for Brekke afer . It nearly drives Aramina mad, and Robinton simply uses it to chat with any friendly, usually-bronze dragon who'll listen.
 * Subverted in Moreta: Dragonlady of Pern: Recorded history says the titular heroine could speak to all dragons. In truth she could not, and that was both in an emergency and with a particularly close friendship between the two dragonriders. That doesn't stop Moreta from feeling guilty about it.
 * Possibly all dragons can talk to all humans. It's just they don't. There are a couple of moments explicable only if a dragon talked to a human who never before or again heard a dragon. The "it's just that they (normally) don't" case is explicitly the way it is with Robinton. The dragons began speaking to him because he had earned their respect.
 * Robinton participated in eye-to-eye talks, Aramina communicates like a dragon, including reception of all broadcasts whether she wants it or not, and Lessa is a true telepath who manipulated humans and dogs and was noticed by all nearby dragons upon "thinking too loud". Pernese gene pool is clearly full of mentasynth mod -- but Eridani methods were said to be barely understandable at best. Maybe not only it doesn't always come to later generations in one piece but combines with Human genetic diversity to fairly random results.
 * It's also rare for a dragon to speak to anyone who's not their rider. Quite a few dragons are pretty chatty with outsiders. It's often used to demonstrate how suitable a potential, non-rider love interest is for a dragonrider ("if my dragon likes them, they must be perfect!"). This undermines the mandate that a dragonrider's first love is their dragon, and no human can compare. It removes any potential jealousy between love interest and dragon by making them friends.
 * "Impressing" (bonding with) a dragon without being formally presented as a potential rider is also a "freak event"; yet in the course of the series we have Jaxom, Mirrim, T'lion and Tai, as well as (arguably) Debera and K'van. It's most likely Rule of Drama. It may be more of an organizational issue after Lessa overhauled everything.
 * Mercedes Lackey's Heralds of Valdemar series features lifebonds, which, in spite of being "incredibly rare", are all over the place in the earlier books of the series. This includes two instances of characters lifebonding again after their first lifebond partner dies, and mention of the possibility of a three-way lifebond. Lackey cuts back considerably on the occurrences of lifebonds in later books, but there's still a character who lifebonds with his own magic telepathic horse.
 * In the Black Jewels series, the Blood (magic-using races) are in the minority among the general population, but all the main characters and 99.9% of the minor characters are Blood. Since the Blood are the ones with magic, it makes sense that they control the government, religion, etc. Landens (ordinary people) barely even show up as servants, although we do see Blood maids, cooks, and butlers. In fact, up until Tangled Webs, a casual reader might overlook the existence of landens altogether.
 * In the Dragonlance novels, Kender are described as being totally fearless, so that when something is just so terrifying that even Tasslehoff is afraid of it, you just know it's a big deal ... until around the third or so time it happens. Then you start to think Kender just have good P.R. guys.

Live Action Television

 * In an example of this happening as There Is Another taken too far, Superman's the Last of His Kind, except there's one more. And then another, and then another, until it was said by fans that Jor-El and Lara are the only people who died on the destruction of Krypton. In Smallville, other Kryptonians are constantly being tripped over, though they tend not to survive the episode.
 * Thankfully, if surprisingly averted in Doctor Who. Maybe it's just in comparison to how many people are accused of being a Time Lord, but, taking into consideration how long the show's been running, there aren't all that many Time Lords.
 * Well, in the classic series there was an entire planet full of them, just not many who got out and about in the universe besides the Doctor. It's only in the new series that Time Lords have been few and far between, the Doctor having been rendered the Last of His Kind  by the Time War.
 * In M*A*S*H, 12-year old Scotch was said to be rare, but people often traded cases or at least bottles of the stuff fairly often.
 * 12-year old Scotch can be purchased today in any liquor store for about $40 a liter. Obtaining it in Korea on the front lines during the war however would be harder to do. It may have been more a case of most combat zone "importers" getting the cheapest stuff they can get, but being open to obtaining higher priced merchandise if the profit is there.

Video Games
"Oh, it's bad luck to be you / a chosen one of many isn't new ..."
 * The Elder Scrolls IV: Oblivion takes this to ridiculous levels. Enemy levels are scaled to yours: this means that grunt bandits with cut-rate, bargain-basement weapons and armor will eventually be wielding the fabled Glass equipment, stated in-game to be incredibly rare. Even if you can accept that there is somehow enough Glass to go around, they nonetheless fight like ordinary bandits, so this leaves us another question: how the hell did they get this equipment in the first place, seeing how beating these guys up and selling their armor is one of the best ways of making money in the game?
 * It gets worse by the time they start wearing Daedric armor, which can only be obtained by killing a powerful demon.
 * Dragon Age Origins prominently features The Joining, a ritual that gives Grey Wardens their powers, but also has a reasonable chance to kill them. In the main game, this trope is averted--fully half of those who take The Joining onscreen (including you) do not survive the ritual. In the expansion, however, almost every character in your party takes The Joining, and only one dies from it.
 * From Magical Starsign, the Celestial Swap spell, which lets the user . When it's first used by Master Chard, it's treated like an awe-inspiring display of power. Then your teacher Madeline (a mysterious and very powerful mage who also taught Chard) gives you a book which you can learn the spell from. But the spell starts to become increasingly common around the halfway point; by the end of the game, nearly every boss and several random monsters can use Celestial Swap.
 * The psychic-and-Warp-power-nullifying Blanks from the Warhammer 40000 universe. They're held up to be vanishingly rare, yet they show up in almost any fiction not primarily starring the Adeptus Astartes. Jurgen.
 * The remake of The Bard's Tale uses this as a Running Gag

Web Original

 * In Paradise, even though only 1% of those who change into Funny Animal forms also change gender at the same time, and even fewer change gender multiple times, the wish-fulfillment nature of the setting means that a remarkable number of gender-changed (and a couple of multiple-gender-change) furries are represented in the stories, particularly as main characters.
 * Also, two gender-changed characters falling in love happens more often than one might expect.
 * A Justified Trope in the sense that the Change is happening to everybody, and it's therefore normal. But the Gender Bender does not. Also, the Gender Changed would band together in support groups and deep relationships would naturally result.

Film

 * In Kung Fu Hustle, the lead character is obsessed with mastering kung fu. Naturally, it turns out all his enemies, friends, and neighbors are secretly kung fu experts of varying ability.

Western Animation

 * A similar phenomenon existed in Teenage Mutant Ninja Turtles, with the Turtles encountering many, many, one-shot characters and extraordinary objects that had a turtle-related theme. There was no in-story reason why so many extraterrestrial aliens, ancient artifacts, and so on should bear resemblances to a turtle, but somehow, the Turtles kept on meeting up with other turtles. Also the long lost sister Venus de Milo. Remember Venus? She had the baby blue mask.
 * How many new gargoyle clans did Goliath end up meeting during the Gargoyles World Tour Arc? It turns out that gargoyle clans actually aren't that rare. Goliath just thought that they were the only ones left.
 * According to the canonical comic, the London clan is actually the largest clan left in the world with more than a hundred members---we just don't see the rest on the TV series. Word of God says that, given the time to tell the full story he planned, there would have wound up being twelve clans in the world (though some of those would be founded during the series rather than already extant).
 * Word of God also puts the worldwide gargoyle population at about 400, so while the Manhattan Clan aren't the Last Of Their Kind, the species is still probably going to be on the endangered species list for a while, especially with their weird breeding issues (a female can only lay one egg every twenty years).