...Not to get weird and dark on a useful/amuzing writing post, but...
Years and years ago, I read someone's experience of finding out that his mom's boyfriend was a serial killer. How much it sickened him to put together odd bits and pieces of their experiences together, recontextualizing them, suddenly understanding new and horrifying things.
But while that was awful, what really fucked him up later wasn't the clues he'd missed or anything-- it was that, one time, they'd been working together on some kind of home project, and he'd been on a ladder and suddenly gotten off balance-- and his mom's boyfriend had immediately reached out, yanked him back, both of them frightened and swearing and then gasping in the aftershocks of panic, and how grateful he'd been that the boyfriend had been there, how they'd both started laughing as the adrenaline washed through them and out again, hugging fiercely, how grateful he still was that the boyfriend had been there, because he owed his life to this man, this almost-father that had kept him safe and had been afraid for him, and the cognitive dissonance of that, the visceral disgust and the aching love and what it meant to be beholden to a monster for the gift of that moment--
And that's why we need to practice the little lies of fiction, where we can see that characters may not always be rendered in black and white-- it helps us learn how to live in a world that may serve us the worst people we may ever know doing us the greatest kindness of our lives.