A good book should cast a spell over the reader. The reader should be drawn into the story, should be so engrossed in it that they're more seeing and hearing the events on the page than they are reading them. A good book should be experienced.
Maintaining this spell is the primary job of the author. When I'm writing, I'm thinking about this more than anything. Everything that hits the page, perfect or not, should serve this purpose.
And one of the most often-cited causes of breaking the literary spell is head-hopping, or a sudden change in point of view. You must establish your point of view early on and maintain consistency, even if that consistency means moving from one point of view to another. As long as it's done seamlessly, and as long as you continue to do it in the same manner, the spell remains intact.
But point of view isn't the only way to sustain or break the spell. Sudden changes in location, time, etc. are also jarring for the reader. Sometimes too jarring. Now, all stories need transitions. It's just the way of things. One scene ends while another begins. Characters move from one location to another. Maybe characters die. But these are okay because they are natural and intended transitions. They jar the reader, but only a little bit. And that's okay.
The problem is when these transitions are unnatural and perhaps even entirely accidental. Perhaps you're writing in one point of view one moment, then dip into another for just a paragraph. Perhaps this is the only spot in the book where you do so. If this is true, you are almost surely breaking the spell you've woven, and this will not serve you well. And it's not just about point of view (though some so-called 'experts' would have you think so).
One of the other ways to quickly break the literary spell is to have a character do something they'd never do. Readers like characters. They depend on them. And they need those characters to act...well, in character. If your hero always jumps into a situation to save the damsel in distress, then suddenly doesn't because you think it serves the plot, expect your readers to be jarred out of the story completely. Plot is secondary sometimes, and it's important to recognize when this might be the case.
So if you're writing a novel of any kind, remember that you're really doing more than that. You're casting a spell, or trying to. Your job, as a writer, is to keep the reader's attention for as long as is necessary to tell the story. Craft your words carefully to avoid breaking your spell unnecessarily.
