One of the most common errors we see in amateur manuscripts is POV slips, which occur when a writer who means to be writing in character POV includes something the POV character can’t know.
For example, if you’re writing from the POV of a starship captain, you ought not put a line like this:
The captain had no way of knowing a massive asteroid was hurtling toward his ship.
If he has no way of knowing, you can’t tell me.
I think there are two reasons this kind of slip happens. First, there’s just bad teaching. Some of the old writing books say you can do this as long as you’re writing in third person instead of first person. Baloney. It doesn’t matter what person you’re using. If you are in the character’s POV you may only reveal information known to the character.
Second, we make these kind of slips because we’re steeped in the novels of the nineteenth and early twentieth centuries, which were written in omniscient POV and therefore did this kind of thing all the time.
The reason omniscient POV is out of fashion is that readers don’t want to see the coming trouble telegraphed. They want to be in the moment with the captain.
“I never did finish Moby Dick,” the captain said, “because—”
A mighty rumble like thunder cut him off. The entire vessel shuddered. Lights flickered, and the blare of klaxons filled the bridge.
The navigation officer gripped the arms of her chair. “What was that?”
The captain spun toward his chief engineer. “Status report!”