"...Why did you include three video games on a list filled with anime characters? Unless they've read about them or own them, nobody's going to get anything you reference from them! Pretty shallow thinking, including your own personal tastes in this story idea~..."
Fans of a particular work or medium see things differently from people who aren't fans of the same things. For instance, a fan might assume that the work they are a fan of is much better known than it actually is. Or, conversely, they might assume that nobody knows a different work simply because they and their circle never heard of it. The fan's perspective is a little warped because they are so close to certain materials and so distanced from others.
Fan myopia is aided and abetted by having a circle of friends who share a narrow interest, making it seem much less obscure than it is. The Internet can be an enabler here: If you spend all your time talking to people who are fans of the same things you like, it's easy to jump from there — even unconsciously — to the assumption that everyone is a fan of the same things you like.
Even when an interest is shared by a young person's entire generation, it might well be unheard of in other, older demographics and vice-versa. This, too, is a kind of fan myopia. Fan myopia also can lead to over-enthusiasm for the work and related works ("This show is the best thing ever!" "Every other medium is garbage!") and so on. This happens more easily to younger fans than older ones who have, over time, seen works come and go and who have even seen media come and go.
Compare Opinion Myopia, for when people feel strongly about something and expect everyone else to feel the same way. Getting too blinded by Fan Myopia can lead to Fan Dumb; all the variations of Fan Dumb, after all, are essentially caused by the fan in question having simply lost perspective on exactly how important something in the fandom is.
Fan Myopia can lead to behaviors such as:
Failing to realize that a joke in their favorite comedy is actually a reference to something that was already famous. Usually an effect of being too young to have known the source of the reference, but definitely a kind of myopia.
Failing to understand why a cherished TV show was canceled, or why a book, movie, or video game doesn't sell highly, when in fact hardly anyone was interested in it aside from its cult fanbase. It's even conceivable that it wasn't Screwed by the Network, but rather it simply didn't draw enough interest to stay afloat.
Being appalled when the creator or writer of a show/song/book doesn't know as much as the fan knows about their work, and seemingly isn't interested in something they wrote or starred in many years earlier. Perhaps an effect of assuming that the creator shares exactly the same attitudes as the fans. This can lead to fans thinking they know the show better than the people who created it. Also leads to accusations of selling out just because somebody stopped writing obscure cult music or TV and became more mainstream. Parodied on Saturday Night Live in the famous "Get A Life!" sketch with William Shatner. In the sketch, a Trekkie brings up the scene from the Star Trek: The Original Series episode "This Side of Paradise" when Kirk gets his effects out of a safe. It turns out the fan wants to know what the combination on the safe was and, of course, Shatner has no clue.
This was probably inspired by several Real Life incidents at Star Trek conventions where various actors were asked highly technical questions about various gadgets featured on the show. For instance, James Doohan got asked so many times about how things like warp drive or the transporter worked that he actually made up explanations to reply to those questions with.
Telling their fandom in-jokes constantly, seemingly unaware that most of the people who are listening/reading won't understand what they are running on about.
Assuming that their favored work (or media, or genre, etc.) is superior to and/or "different" from all other similar types of work, media, or genre, not realizing that their favored work (or media, or genre, etc.) is, in fact, very similar to all similar works.
Assuming that the work is known worldwide. For an example, lots of Anime series which are known in the United States and Japan aren't well known outside. It may be surprising for fans to hear that series like Haruhi Suzumiya and Neon Genesis Evangelion aren't that well known outside a few selected countries, or even in the countries where they are available.
Assuming that the work somehow "transcends" other examples of the genre simply because they are fans of it.
With respect to certain franchises, fans may occasionally assume the position of "We are your customers and the customers know what they want". Or they may play various appeal cards such as "You wouldn't be here if it weren't for us fans so it belongs to us as much as you".
Insisting that creators and producers should tell the story that the fans want to tell. This story might be a story highlighting their favorite underrepresented character. Or a story that answers certain unanswered questions, shows a backstory, Great Offscreen War or Noodle Incident which was never meant to be shown, or providing closure to a character or incomplete or open ended story. For example, many Star Trek: The Original Series fans are still demanding a canonical final fate for the surviving original characters (while the surviving actors who played them are still alive). This mentality tends to disrupt the artistic integrity of the franchise in question due to the fan (not creator) tendency to treat their favorite franchise as if it were just a product to them (as it is for the studios and sponsors). To non-fans, unanswered questions, ambiguous endings, and interesting characters or subplots that don't get enough screentime are integral parts of any story and force us to use our imagination to fill in the blanks. And beloved characters, whether they get closure or not, leave the stage when their story has been told.
Many Doctor Who fans refuse to take "no" for an answer whenever they ask producers Davies or Moffat about the series ever showing the Great Time War or the fate of the 8th Doctor.
A significant number of Robotech fans insist that it is Harmony Gold's duty to satisfy its customers (ahem...fans) by going back and completing The Sentinels (which will never happen).
Related to the above is the inverse; not wanting a story to be told the way it is intended to be or should be told just because it clashes with the fan's preferred story, no matter how unlikely it is that their preferred story will ever happen. For example, fans of a particular shipping pairing naturally want their preferred ship to hook up as soon as possible, but if that pairing were to get together straight away with absolutely no complications, hardships or difficulties whatsoever, the story of their romance wouldn't be a particularly exciting or interesting one. Any difficulties they might face, however, will result in a chorus of pained howling. And that's in the case of the Official Couple; those who follow a pairing that has no chance in hell of ever happening can react even more passionately when the creators try to remind them that it's never going to happen, even if there are perfectly sound and logical reasons why it's never going to happen. Similarly, those who have built up a particular piece of Fanon up to the point where they're convinced it's fundamental to the story can react with genuine betrayal if the storyteller casually takes a direction that completely wipes the Fanon out of existence.
With franchises that last several generations, it is inevitable that the reins of power over creation and production will be passed on to new individuals, some of whom may not have been born when the franchise began and are tasked with keeping said franchise up to date and relevant. Typically, the original creator/producer is deceased so fans take it upon themselves to decide whether or not "he" would approve of the direction the current producer is taking with "his" creation. This includes the obvious nerd fare like Star Trek, but also - and somewhat surprisingly - kids' shows like Thomas the Tank Engine.
In anticipation of angry reactions to the above sentence, refusing to acknowledge that a work was intended for children. Many perfectly respectable works were intended for children, and many of them are still enjoyable when you're an adult, yes, but (to pick a random example) Sonic Sat AM was still a kids' show, and acknowledging that doesn't reduce the work's quality. In fact, one might even argue that attracting a Periphery Demographic is a symptom of higher quality.
Tropers are not immune to Fan Myopia, nor do they claim to be. Indeed, much of this wiki could not have come about if it weren't for zealous fans of television and other media. However, generalizing from your own experience is usually a bad idea. Assuming that other people know more than they do can result in incomprehensible attempts at Two Words: Obvious Trope or similar, or telling the world that the ending to something is It Was His Sled when it wasn't, really.
Citing examples of characters or episodes without explaining what work they're talking about, because "surely everyone knows what I'm referring to". ("Cheetahmen II. Nuff said.")
Committing the infamous "How could this trope go so long without mentioning Show X?" word cruft.
Pot Holing to the characters/situations/quotes without identifying the work they come from out of the belief that it's so Self Explanatory that everyone's seen it and knows instantly who or what is being discussed.
Assuming that their favored work (or media, or genre, etc.) is the ultimate example of everything — or at least, the ultimate example of everything the fan thinks is good. On this wiki, at least, this tends to lead to misguided Entry Pimping and forced attempts to present the show as an example of a particular 'good' trope even if the show in question does not actually use or reflect that trope, whilst over-protectively justifying or even outright deleting a show's entry in a 'bad' trope regardless of how fair or accurate the example from the show is.
Mentioning a specific example without indicating in what episode/book it appeared, making it hard to look up exactly where it happened.
Comparing an example with a similar example from another series, with implications that they will know because it's so widespread.
Adding an example without mentioning what series it's from.