You’re GMing a fantasy RPG, and the PCs need to get through a door. A simple wooden door; but the door is locked. Can they pick the lock? Can they bust it down? Can they burn it? Could they remove the hinges? (If the hinges can just be removed, then why don’t thieves always choose that method to get past doors, rather than bothering to pick locks?) What about tapping the hinges? Does the door even have hinges? How do you make a door without hinges? How accessible are the hinges?

All of these questions can be difficult for a GM (or other person with narrative/worldbuilding control) to answer in the moment. Unless you happen to personally be an expert in both lock-picking and door construction, you may not have a good answer for your players’ questions. If the door opens in, away from the PCs, that implies it must be easier to bust down; but if it opens out, toward the PCs, that implies that the hinges must be exposed to the PCs and thus defeatable, at least given tools and time. (Cue the classic visual gag of someone boarding up what they think is an inward-opening door, only for the adversary to just open the door by pulling outward.)

Of course, the GM can just say “I don’t know how the door works, but it does; and your character has the background to know how to deal with it, so you deal with it. I don’t know how you deal with it, but you do.” But that can be a very dissatisfying answer for players and GMs who want consistency, immersion, understandability, or, y’know, ‘realism’. You can, of course, set those concerns aside, or not have them in the first place. But that can be dissatisfying or confusing, for those trying to understand what’s possible within the ways of how the game world works.

This, then, implies something very tricky about RPGs: To the extent that your table demands that consistency/immersion/realism, the GM has to know how everything in the world works. How hinges work, how many people it takes to work a smithy, how you make a book completely from scratch, how much land a single ox team can work in a day, how quickly lamp oil can soak into a cloak, how much Sashtian you can read if you only really know Morensian, how possible it is to identify an individual bird by its feathers, and every other thing in the game.

Obviously, the vast majority of those questions don’t come up most of the time; and no one is going to demand rigorous realism about everything.

But I note that this is still a big difference between RPGs and, for example, prose fiction. In prose fiction, if the author needs to know how hinges work, or how strong medieval glue is, or whatever other thing, they can go away and research the question; or they can, potentially, steer the narrative away from the question, or smooth it over: “She made a few quick, subtle movements, and the door swung open.” No need to explain the mechanics of the lock. But in RPGs, the entire plot can sometimes hinge on exactly how hinges work. The GM can, yes, just kind of smooth it over; but the more realism, consistency, and immersion the game is trying for, the more the players need to know all their options, and the more the GM needs to know how all those things work. And it’s probably not great if the GM stops the game to do an hour of research on how hinges work. Certainly, “you figure it out somehow, and after the session, I’m going to go figure out how hinges work” is an option, but still, in the moment, it can be a little dissatisfying.

All those questions become that much more difficult to answer if it’s a high-tech setting. Like, how does an airlock door on a space vehicle work? Is there a way to lock it? If there isn’t a way to lock it, is there any way to prevent access to the inside? If there is a way to lock it, how does that work? If the door is electronically locked, does it have access buttons/ports/pads/whatever on both the outside and the inside? If the access device is only on the inside, then how does a crew-member who gets stranded outside ever get back in? And even if you as the GM understand how an airlock door works, what about a supercomputer? What about a fusion drive? A laser sword? What about a reframulating dehisticator, or a Zhang-Reyes Manifold Theory device?

Those questions generally multiply with higher tech levels. The more complex the world is, the less each of us understands how exactly it all works. If a door hinge implies a big basket of questions about how it works, then a higher-tech thing implies that many more baskets of questions.

Don’t the questions also multiply with magic? Well, maybe. That’s the thing about magic, though: I think it’s generally allowed to just say “we don’t need to explain how the magic works; it just does”. In many ways, “magic” is a synonym for “we’re going to suspend consistency/immersion/realism here”. “A wizard did it” and all that. Certainly in B&C, I’ve tried to keep magic consistent, but also mysterious. It’s okay to not know some of how it works, including what’s possible for a specific magnitude of spell.

So I think all this explains a large part of the appeal of the fantasy. As I’ve said in other contexts, I might not understand how the compass in my cellphone works, or how to extrude aluminum; I sure as heck don’t understand how antigravity or blasters work. But I basically understand how a sword works. If the players want consistency/immersion/realism out of the game, then a pretty sure-fire way to do this is to stick to a lower tech level. Introducing additional tech multiplies questions.