One of the hardest things to do in fantasy writing is to deny your characters what they want.
There’s a brilliant scene in The Princess Bride that demonstrates this. In it, Inigo, Fezzik, and the Man in Black have to figure out how to get through a castle gate that has but one gate key and is guarded by sixty men. The scene goes like this:
Fezzik: You just shook your head -- that doesn't make you happy?
The Man in Black: My brains, his steel, and your strength against sixty men, and you think a little head jiggle is supposed to make me happy? I mean, if we only had a wheelbarrow, that would be something.
Inigo: Where did we put that wheelbarrow the Albino had?
Fezzik: Over the Albino, I think.
At this point we think: “Oh, how clever!” Earlier in the movie, of course, there is in fact a wheelbarrow and it is a necessary part of the Man in Black’s solution. The scene, however, continues, resulting in, for me, one of the funniest moments in the entire movie:
The Man in Black: Well, why didn't you list that among our assets in the first place? What I wouldn't give for a holocaust cloak.
Inigo: There we cannot help you.
Fezzik: (pulling one out) Will this do?
Inigo: Where did you get that?
Fezzik: At Miracle Max’s. It fit so nice, he said I could keep it.
A holocaust cloak is, from what I can tell, a magically imbued cloak that protects its wearer from fire. It turns out to be the exact thing the Man in Black needs for his plan, and of course, there’s absolutely no prior justification for Fezzik having one (especially one that fits him).
The joke, of course, is that a fantasy writer can create solutions to whatever problems their characters might have. Need a wheelbarrow? It’s easy enough to establish the presence of a wheelbarrow. Need a holocaust cloak? Hey, it’s fantasy. Such things exist!
The problem with this aspect of fantasy is that, if extended to its logical conclusion, it’s nearly impossible to create dramatic tension. There are no difficult problems because magic can solve whatever problems there are.
This is where discipline comes in. As a writer, you have to be disciplined as to the limitations of magic and other powers the characters may have.
A good example is Traxy in my new book, The Elven Comedienne. Traxy is essentially the Elven Goddess of Tricks and Games, and thus has significant powers. One of those powers is to create objects of her choice out of nothing. In one scene, she single-handedly defeats two henchmen using these powers in what I hope people find is a humorous way.
It’s a funny scene, but it presents a problem. Traxy is established as a 7’2” tall muscular forest elf with the power to create objects out of nothing. How can an antagonist hope to defeat her in combat?
That’s where rules come in. I don’t want to spoil the book (or the joke), but let’s just say that Traxy isn’t nearly as effective in subsequent battles. This is a good thing for the book.
That takes discipline as a writer to do. It’s tempting when the protagonist encounters a significant problem to just let magic take care of it, in the way the Man in Black does in the passage quoted above. If magic is always the solution, though, there are no significant problems for the protagonist. And that’s boring.
Boring solutions result in the death of the narrative. As a writer, it’s imperative to not let magic be the solution to significant problems, lest they become insignificant.