I write fantasy so I have to incorporate some magic in there. Many readers of fantasy want magic to be the center of the story and to some degree it has to play a role large enough to distinguish my created world from this one. But how much magic? How powerful should the magic be?
I first fell in love with the fantasy genre in junior high school when one of my teachers lent me her copy of Tolkien's Lord of the Rings. I didn't think about it then, but now that I write my own books, create my own worlds and define the laws of magic, I wonder about that story. How did the Rings of Power work? Why couldn't the elves and wizards combine their magical powers and take on the Dark Lord? How did the One Ring rule them all?
I can still enjoy the books without knowing these things but I do wonder. I've read other fantasy novels where the magic of one side seems so powerful it seems they should be able to win with a wave of their hand. But that would make for a short book. There must be some limitations to the magic or at least to the person or persons using it. The author gets to determine those limits.
Is the magic limited by the strength of the wielder? Or is the use of magic limited by the damage to the entire existence of life if it's overused? Is the magic limited by some force on the opposing side? Is the magic limited by the knowledge of the magician? What is the source of the magic? Can it be used up? Can its use injure the user? Are there moral reasons for limiting its use?
I would think writers of science fiction have to ask similar questions about technology in their novels. There have to be limitations or it's no fun.
Have you read a novel where the magic or technology was so overwhelming in its power it ruined the novel? What limitations have you used or seen used in an effective way?