Option 1: We require more minerals
My character in Final Fantasy XIV isn't just good with a gun; she owns one. It's more of a showpiece than anything, but it's perfectly functional. So why in the world doesn't she use it all the time? Partly because a gun's no good without ammunition.
Sometimes we forget that a lot of technology requires certain things to function correctly. Your smartphone could dazzle a whole lot of Elizabethan English people if you traveled back in time, but it would still run out of battery power and then you'd be facing something of a problem. Similarly, if you're trying to build a gun when you shouldn't be able to, the problem might not be lack of knowledge but a lack of metal suitable for casting an actual barrel.
This helps explain why your character's possessions aren't in constant use. Imagine a character in Star Trek Online with a highly experimental weapon that can disable an entire room when necessary. It's certainly useful, but it's built on unknown technology that will eventually wear down and break. Replicating it doesn't work, and so you're left with the reality that each use is one step closer to never being able to use it again.
It's not enough to have something; sometimes you just don't have the juice to use it on a regular basis. A gun without bullets is an inelegant club. It explains nicely why you don't use it, especially if you expect at some point to have access to it naturally, at which point the resources just became more available.
Option 2: The world doesn't support it
Your Trooper specializes in melee combat, you stay in melee, so why exactly can't you wield one of Star Wars: The Old Republic's techblades? Well, you do know how, but as it happens the realities of field maintenance make it impractical to use them on a regular basis. Most facilities maintain rifles but don't pay attention to blades for soldiers. So for convenience, you stick to your gun.
This one is a bit more of a stretch, but it works just as well. Yes, your World of Warcraft Paladin knows how to wield two weapons, but there's a real stigma attached to it, or maybe she just doesn't have an easy time finding appropriate weapons that are properly balanced for her techniques. She uses the tools she has rather than the ones she would theoretically use in a perfect world.
Where the previous option can explain something you can do or use irregularly, logically, this explains why you're never seen using something. It fits nicely for potentially ambiguous elements that may or may not ever come to the game proper. You may never be able to wield techblades, but that just means that the status quo never changed in the least. If you are able to, well, there was a paradigm shift. Again, it mirrors the real world pretty well; there are a lot of things that are possible to do in theory but don't work out in practice. In theory you'd drink nothing but microbrewed beers, but in practice it's just too cost-prohibitive, so you grab something more accessible.
Option 3: Alternate interpretation
One of my characters in World of Warcraft was not actually a Paladin. He was an engineer with a number of gadgets at his disposal, ranging from a portable force shield generator to molecular reconstitution beams to weapon with various setting enhancements. Oh, all of his tricks looked a lot like Paladin abilities, but that was more of a happy accident than anything.
This one is inelegant and kludgy and not something to be used eagerly. You're essentially telling everyone to disregard obvious information. Sometimes it works out easily -- claiming that your character isn't really a Jedi, for example, just requires ignoring a class tag as long as you dress the part. Other times it requires ignoring a lot of mechanics and obvious visual cues, which means you either have to go out of your way to minimize those cues or have to ask others to pretend that they didn't see the obvious.
But the benefit is that you don't have to explain why a character doesn't do something; he does it. He's doing it right now. Why wouldn't an engineer use his tricks in combat more often? Well, he does. You read it as being something other than it was, but that's down to you, not anyone else. Maybe you should have asked first.
Feedback, as always, is welcome down in the comments below or via mail to firstname.lastname@example.org. Next week, I want to talk about tapping on the fourth wall, for good and for ill. The week after that it's time to talk about when it's the time to cut ties with another roleplayer.
Every Friday, Eliot Lefebvre fills a column up with excellent advice on investing money, writing award-winning novels, and being elected to public office. Then he removes all of that, and you're left with Storyboard, which focuses on roleplaying in MMOs. It won't help you get elected, but it will help you pretend you did. If you need a refresher, check out the Storyboard Library.