Okay, I've talked about characters for a while. Another aspect of writing that's important is point of view. There are various types of point of view, but the one that's in favor just now is third person tight. That's where the writer (and therefore the reader) sees everything through one person's eyes, so to speak. If that person doesn't hear it, doesn't see it, then the reader doesn't know about it, either. The writer gets around this by changing to another character as the PoV character, someone who will hear or see the important things that the reader needs to know about.
A good writer only changes his PoV character at a point where the scene changes.
What work I've done with Mac's story has definitely taught me to do a tight PoV, and to only change PoV character at a scene change. You see, the reader never sees anything from Mac's PoV. Nothing. Each scene is told from the PoV of one of her crewmates.
Remember how I said I'd had to learn quite a bit about a number of her crewmates, and that the history of secondary characters would influence what advice they might give, how they would react? This was particularly true when working on Mac's story; the PoV character's history and personality flavored how he or she perceived everything that Mac said and did.
For instance, her 'adoptive brother' (who was her real brother's roommate when they were all at the Academy) tends to see her as a naïve girl in a woman's body, someone who doesn't quite realize what she's doing that keeps landing her into trouble. Her superior officer (who, we learn through other people, probably reminds her of her overbearing, chauvinistic father) thinks Mac doesn't have a brain in her head, since she can't answer a single question about her field. That confuses the fellow officer tasked with tutoring her, because when she asks Mac the same questions, Mac knows the answers without any hesitation.
Every person on that ship sees Mac in a different light, based on their own history. And yet, there's only one Mac.
But she is complicated. Aren't we all?