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Necessary Weasel

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This is not a Necessary Weasel. It's a Gratuitous Weasel, courtesy of the Rule of Cute.

"Be happy that weasels infest the world. Weasels are like motor oil for society. It wouldn't be fair to judge motor oil outside the context of an engine. If you put motor oil in your mouth, it would be filthy and slimy and leave a bad taste. But when that oil is inside an engine, it does an important job and you're glad it's there. Weasels are the same way. Slimy and disgusting, but essential."
Scott Adams, The Way of the Weasel

As a logical extension of Tropes Are Tools, many tropes that might otherwise come across as gratuitous, offensive or just plain wrong in most genres are considered not just accepted in certain genres, but are practically a part of the genre. Complaining about the simple use of the tropes (as opposed to particularly offensive variations) in said genres is rather short-sighted and pointless, since, well, it's in almost every other work in the genre.

Can often be the cause of an Enforced Trope. Some Acceptable Breaks from Reality are Necessary Weasels to particular genres as well. Also compare the Anthropic Principle, where certain factors, no matter how improbable, have to occur for the story to happen. Contrast with the Writing Pitfall Index, an article listing tropes that can lead to real (versus merely perceived) flaws. See also Trope Enjoyment Loophole, for when somebody's Pet-Peeve Trope is handled in a way that makes it no longer annoying (or vice versa).


A related concept is the doctrine of scènes à faire in some countries' copyright law. This doctrine denies copyright protection to elements that are considered necessary to a genre or setting. For example, a court of appeals in the United States has held that a movie set in the South Bronx is expected to show certain features associated with the South Bronx at the time in which the movie is set and that showing such features is therefore not copyrightable expression.


Artistic "flaws":

  • Rule of Cool in general; "realistic" does not always equal "interesting."
  • More Dakka, Stuff Blowing Up in summer action films.
  • Invincible Heroes in combat-oriented video games. Depending on the difficulty at least (or the player's skill).
  • Clean, Pretty Childbirth in family friendly films (and family friendly TV shows). Most people do not want to see body fluids and other gross things during a birth, particularly during scenes intended to be heartwarming, and it usually is required to be omitted to keep the rating.
  • Toilet Humor in comedies featuring babies (see The Diaper Change, Improvised Diaper, and Tinkle in the Eye) or animals (see Road Apples, Urine Trouble, and Toilet-Drinking Dog Gag).
  • An Audience Surrogate character in a Harem anime.
  • Anticlimax Boss in Wide-Open Sandbox games. If a boss must be fought, and players can be optimized for something other than combat, then the boss must be beatable by the weakest character who can reach the fight.
  • Boss Arena Idiocy because they would be frustratingly hard or Unwinnable otherwise.
  • Purple Is the New Black, and any other specific attributions of a particular colour to light or darkness (like blue or red).
  • The Gods Must Be Lazy and similar tropes, like God's Hands Are Tied and Have You Seen My God? in settings where vastly powerful deitie(s) exist. Such tropes preserve conflict by keeping the story from favoring the good side too much by making it too powerful, and allow for a human underdog hero to step in when the god(s) cannot or won't.
  • Just Hit Him: There would be no story if The Brute simply punched a hole through the hero's chest, instead of dramatically tossing him around the room.
  • Will They or Won't They? in stories involving the main character picking a Love Interest. Unless there's something else to generate conflict, this trope will be used to keep the story from ending until They Do.
  • Common Hollywood Sex Traits: Because real sex isn't always sexy, and a realistic depiction would likely go into Ikea Erotica territory, most stories that feature sex or its aftermath are going to involve Idealized Sex. An exception is when the sex is played for comedy instead of titillation.
  • The Coconut Effect: A sound effect, color, etc., that people expect to be there, such as horses' hooves that sound like coconuts being smacked together.
  • Many Christmas stories involving Santa Claus do not address or adequately explain Plot Holes inherent in the premise, such as why no adults know he exists even though there are millions of toys showing up that nobody purchased, among other questions. Attempting to answer these questions may diverge the story too far from the classic legend, and most people who like Christmas stories are willing to ignore these issues. Sometimes, the story does answer the questions, but these stories make it clear from the get-go that they're not your grandma's Christmas stories.
  • Rubber-Band A.I.: In various genres, but especially the Racing Game genre. Quite simply, if you're able to do so well in a video game that the AI has no hope of beating you, the game gets boring. So sometimes, it's necessary to make the AI cheat a little bit to keep the game challenging.
  • Plot Armor: In action or adventure stories, if no main characters ever put themselves in risky situations where their lives were on the line at least sometimes, the adventure and characters would probably be really boring, but at least some of them also have to survive these situations even despite unlikely odds because otherwise they wouldn't be main characters and the story wouldn't be able to continue.
  • Stock Light-Novel Hero: See the Analysis page for how the constraints of the genre have molded this trope. Like an Invincible Hero in an action game, a man who just happens to have enough skills or luck to thrive to some degree when placed in an implausible situation is necessary, otherwise we would be reading about how a man gets torn apart by demons in thirty seconds and readers would really prefer to believe that they would be better than that if placed in a similar situation.
  • Historical Hero Upgrade: If every real or mythological figure was portrayed as accurately as possible, the vast majority of these historical persons would be too morally repugnant for a modern audience to root for.
  • Dramatization/Very Loosely Based on a True Story: Real Life is not like fiction. There are many boring parts, there's no real story arc, often many internal inconsistencies and details that are confusing for outside viewers, and as noted above, some "protagonists" may have done stuff that would make it difficult to root for them if it were a story while "antagonists" are rarely as black and white as fiction tends to make them. Changing details for stories supposedly Based on a True Story is required to make them fit into a cohesive and entertaining narrative (although contention can come from how much and what parts are changed from real-life events).
  • Infodump: Sometimes, the audience will need to know something critical before it happens and, while usually a lot better to try and work it into the story gradually and over its course before it becomes relevant, there are some situations where it's just not possible without bloating and/or slowing the pace of the main plot to a crawl.
  • Musical World Hypotheses: In some musicals, it makes sense that the characters are actually singing, while in others, it would make more sense if they were just imagining it.