That’s the question for fiction writers. And it’s both complex and crucial. What we call "point of view violations" affect credibility and thus reader response from the first sentence to the last.
Tip: Anything perceived as a point of view violation is one, and anything not? Isn’t.
Individual readers will be more or less tolerant. But to avoid Hamlet’s indecision and the contamination of “something rotten" in the state of your fiction, accept that certain violations are just violations. If this seems harsh, I’m “cruel only to be kind.” Watch out for these:
~ Switching from one point of view character to another without justification.
Most readers cheerfully accept consistent and graceful use of two or more perspectives. But abrupt or unwarranted shifts are impossible to hide: they feel like violations.
~ Using 3rd person (“he,” “she,” “it”) and first (“I”) interchangeably.
Every reader will squirm at “Ali loved barns. I’d love to inhabit a converted one, she thought.” That second sentence requires italics or quotation marks. Better yet? The consistency of “Ali loved barns and dreamed of inhabiting a converted one.”
~ Offering inauthentic observations.
Characters can’t explain what they never saw, can’t possibly know, or wouldn’t admit.
But characters can guess. and readers delight in watching them do so. How does that work?
* Let characters infer from physical cues.
If Marcy tells readers what Alain thinks, that's a violation. If Marcy observes that he draws close, pulls away, and repeats this over
and over, this is more an accurate assessment that he's ambivalent about kissing her than a violation.
* Clarify the distinction between narrator and character.
Start a new paragraph. To make the shift from close to the character to further away, use a transition to bridge the gap. Here's an
Sam hated snakes and knew that numerous species inhabited every continent.
Kenya, where Sam was stationed, was home to five of the deadliest vipers in the world.
* Expand point of view restrictions consistently rather than inadvertently.
Is whatever sleight of hand you want to execute legitimate? If so, make readers believe it.
In the end, point of view resembles every other aspect of fiction. Set things up meticulously, and you’ll surprise readers so much that you can get away with a lot. Not everything, though.