Magic writers are able to get away with more plot holes than their peers because illogic and inconsistencies can be explained as magic. Even then, there is a thing such as overdoing it and stretching a reader’s imagination so far such that the whole thing becomes absurd. Having rules for magic systems keeps the readers in the realm of fantasy without having them question the whole thing and see it as implausible, unbelievable and inconsistent. Here is why an author would be well advised to introduce rules for a magic system.
Characters are forced to work for alternative solutions
A story where all characters’ challenges are solved by Deus ex Machina soon becomes an anticlimax. Limiting magic forces that characters to use their guile, cunning, intelligence and other traits to overcome the challenges that face them. Magic is a tool that gives them a bit of an edge over other characters, which also places more impetus on the oppressed character to find a way to defeat this edge.
It helps to focus on the characters and not the magic
A writer should remember that a magic story is not about the magic but rather the characters in the story. The magic is a prop to help them achieve their motives, good or bad. Focusing too much on the magic, how it works, who owns it and so on makes the story read like a magic-making manual instead of a story with protagonists, antagonists, and their motives.
Limitation brings out character weaknesses
The Gorgon Medusa’s weakness was seeing herself in a mirror. This was what was eventually used to destroy her. Limiting the magic powers of a character leaves them susceptible to a weakness which the opposition can exploit. It is a way of leveling the field for both protagonists and antagonists such that there are ebbs and flows in the story, just like happens in real-life where the powerful are sometimes brought down by the weak through foolishness, indiscretion, and other human weaknesses. This makes the story more believable.
It shows the uniqueness of the magic
If magic was freely available to all antagonists and protagonists, there would be no story because the story becomes just another narration of ordinary events, like humans having a dialogue (using speech). There is nothing unique in this. But introducing limits to who can own the magic makes the story unique in bringing up sub-plots on how different characters learn and use the magic. If Neo was born knowing that he was the ‘One’ there would be no Matrix.
I think rules to magic systems means everything is not too easy. If magic could fix everything why even have a story? Am I right? Let me know your thoughts in the comments!