" And some go the other way, the most lethal way of all: when the pressure gets to be too much, it's not their nerve that breaks, it's their fear. They lose the capacity to be afraid, even when they should be. These can't ever go home again. They're like those First World War airmen, the finest ones, shining in their recklessness and invincible, who got home and found that home had no place for what they were. Some people are undercovers all the way to the bone; the job has taken them whole. "

― Tana French , The Likeness (Dublin Murder Squad, #2)