As with all most rules: if you’re able to make the story work without it, go for it. But most writing “rules” exist because a lot of writers need guardrails to keep them on the path. I think it’s easy for a lot of people to get off track and too focused on the wrong plot lines and sources of conflict, since there are often many going on at one time. So keeping your eye on the central conflict (whatever that may be) can keep the story focused with a minimum of wandering :).

I think that’s an easy assumption to make, since our characters are always in conflict with other characters. But there’s often something underlying that is creating those relationship problems.

I thought all my novels were character vs. character…but now that I examine them, several have character vs. self at least as much as another character.