People are photons. They exhibit a particle-wave duality. When no one is watching, they act one way, they act many ways. Their actions are unpredictable and varied. The possibilities are endless.
Observe them, and they act uniformly. It's in their nature. When a person knows they're being watched, they become governed by the rules that govern society.
Characters are like that too.
Until the moment we write them down, their possibilities are endless. They can act in ways that are both contradictory to what we know about them, and completely in line with who they are.