> No need for "serious justification" unless you're trying to pull it out of nowhere halfway through the plot. If it's there from the start, there's no problem.

Yeah I think most readers care more about consistency than realism. Being completely realistic makes consistency easy but a harder sell in terms of entertainment.

Maybe one way to view consistency is modelling the story world as a network of criss-crossing character threads. Where one axis is time and the other(s) are uh something? Anyways, consistency is how predictable (smooth / linear) the thread is. We follow the main character's thread pretty closely so that thread is allowed to suddenly curve (plot twist) without risk of losing the reader. We only catch glimpses of the supporting cast / antagonist so those have to be either predictable or the narrator has to backtrack and reveal any twists where necessary. And maybe how intricate yet well-behaved this network appears is what gives the feeling of stories coming alive. Or maybe I'm just on too much caffeine and ranting.