Completely arbitrarily, as far as anyone can guess. The, um. The Not-Them feeds on fear, obviously, of. Someone being very obviously wrong. Not who it's supposed to be. But for that to work, someone has to know.

[He's not sure how he'd feel if it had been him, who'd been stuck knowing. He might have snapped a lot earlier.]

Martin and I didn't learn the truth until we saw it turning into a monster to go hunting Jon.