Writing a book can inspire very strange conversations, especially when that book isn’t centered in reality as we know it.
The reality of the book should have its own rules, for what is reality if not a consistency of experience, the blending of the physical and metaphysical into an established congeal of, well, everything.
A book does not offer a totality of a world, but a glimpse into it. And that glimpse should be consistent. You don’t have to lay the ground rules for everything, but you do have to lay the ground rules for everything the reader is going to glimpse. And in doing so, you must also lay the ground rules for things the reader may never even think about, but those things must be established because firstly they give a truth to the things the reader does see, like how an iceberg is very real and seen above the surface only because of the existence of the bulk of it below the waves.
And second, who’s to say where the readers eye may wander?
The writer guides, walks a fine line between hand holding and herding, but you can’t put blinders on the reader. A good world, a true world, is one established well beyond the boundaries of where the story is actually written.
And so a good story doesn’t excuse inconsistencies by saying, “A wizard did it!”
Unless a wizard actually did.