Severus Snape based on his description in the books versus the singular depiction of that character in the movies, as played by Alan Rickman.
The flip side of this is the other aspect: the fact that the reader is responsible for visualizing everything means that they can end up missing little bits. In a movie, everything that's in a scene is present on some level - the viewer might not notice them immediately, but they're still there. In a book, if the reader forgets something's there, they're not going to visualize it. In addition, if the reader doesn't know what something's supposed to look like, their imagination can be limited by that fact - and the author can't stop to explain exactly what everything looks like. Certainly imagination and creativity are important, but they can't do the entire job themselves. If you describe something as "warty" or "leathery" or even "green", the person must know what those things are and connect the word to the concept. In contrast, a movie could be watched even by someone who didn't speak any language. This is the kind of conflict that's created between presentation and realism. It's one thing to have something be "accurate", and it's another thing to have it be "immersive". Optimally, the two things would work together, but a misaimed focus can result in one being emphasized far more than the other.
The result of this is that many books can come off as "dry" to readers who don't have that kind of material to refer to. It's one thing to have a very cut-and-dry depiction of combat ("they shot at us, we shot back") and another to actually see and hear the bullets fly. I've said before that movies and games are only able to depict sight and sound, and lack the other three senses. Books, then, can be said to have "no" senses - everything must be connected to an understood experience, in the same way that those "other three senses" must be connected to a movie or game. This is also true of interviews: words can convey a lot of meaning and give a lot of emotional context, but it's not a complete picture. In this interview, Eugene Sledge actually touches on this subject by stating that people don't understand how loud and intense the landings on Peleliu were. Despite some minor issues (see previous limitations on sound and noise), the depiction of that scene in the Pacific attempted to rectify that.
|Shot from "All Quiet on the Western Front" (1979)|
Environments are affected by this, as well. In a video game, for example, a dungeon would be able to have countless little doodads and decorations - at least, if the designers cared to put them in. In a tabletop RPG, the dungeon master would have to address each decoration directly if they were important. If he just said "there are some skulls and stuff" then the players would have differing, but vaguely accurate, views of what the area looks like. However, if those things could be interacted with, then every single thing would have to be listed to allow the players to make decisions about them.
|Actual photograph of German soldiers at Verdun.|
Here's a similar example: it's one thing to say "someone got shot" without providing further detail. It's more of a problem to describe it inaccurately, because if you're not being cartoonish or obviously sarcastic, people have no reason to assume it's not real. Preferably, the information would be accurate, but it's better to have less information than to have inaccurate information. What's worse is when writers, authors, and developers recycle their information from other media, rather than direct sources. This is "worse" because if that information was inaccurate, then that inaccuracy is going to be passed along over and over.
|German Propaganda from WW1. The caption reads "We teach you to run!"|
The same is true of the human body. If you cut someone in fantasy, do they not bleed? If so, are they actually bleeding or are they just sort of spraying blood in a non-descript way? If you open that cut wound, do they not have muscles and bones and organs ? Do they not have to eat and sleep? If all the various sub-aspects of "being a human" are the same, then why is the reaction to stimuli so different? How are we supposed to identify with those "three missing senses" (or five missing senses, in the case of books) when we don't even know if the character has them? How are we supposed to identify with them if their body works completely different than ours?
This is a key concept: to understand a larger picture, and how a larger picture can exist, it must be assembled from smaller concepts. Small items add up to form a costume or uniform, small traits add up to form a character, small facts add up to form plausibility, and small events add up to form a story. Real life is, to oversimplify things, not that complex: it is just exceedingly diverse. All of the things that happen in life can be reduced to simple, understandable equations, but it's the fact that there's so many of them that makes it complex. It's okay if you set a rule differently ("there's magic in this world and it works in one specific way", "the guns in this universe operate like this"), but if you deviate from it the world feels less real. If you're relying on reality to provide the base for your universe, then un-noted deviations are going to make the world feel less real.
Of course, this all depends on whether or not the audience specifically knows if something is fake or not. The damaging part about inaccuracy is that people who don't know things make assumptions about what is or is not true, like when over-concerned parents watch Mazes and Monsters and come to the conclusion that D&D is harmful Satan-worship. If it's a simple assumption ("water runs downhill"), it's more likely to be picked up on ("wait, is that water running uphill? Uh, is there an explanation for that?"). If it's a complex subject, such as medicine, biology, economics, physics, and so on, then only specialists in that field are going to understand it, and everyone else is just going to roll with it. This leads to a reinforced understanding of the world that's abjectly inaccurate, not just because the movies are inaccurate, but because people don't know they are.
The issue of accuracy comes from the fact that authors are human beings, and like other human beings can't know everything. However, what they do know can end up being problematic. An author is representing an entire world here - if they could accurately depict everything in the entire world, they wouldn't need to be an author, because they'd be able to do any job ever. "What people know" generally comes from "what people enjoy" - if they like movies, they'll know stuff that comes from movies. A great amount of what a person knows comes from incidental knowledge, rather than directly-studied knowledge, and media needs to start dealing with that.
So to sum up:
1) Books allow for imagination, but also have less room for detail than movies because those details must be specifically noted rather than simply being present.
2) The small details present in a book, movie or game can flesh it out and make it feel more "real", in one manner or another.
3) A movie or game, being "multimedia", can overlay concepts in a way that directly illustrates the intended reality to the audience. In contrast, a book must actively work to create that sort of environment.
4) Inaccuracy is damaging if it is recognized because it calls the "systems" of the universe into question. It can be justified, but should not just be directly ignored.