Usually, they think he lost it in the war. He lets them keep the gruesome fantasies playing behind their well-meaning eyes, because it's not his place to take them. He's full up with his own anyway. In truth, he lost it when he was too young to fight for his country, but just old enough to start fighting for himself.
Jack and the twentieth century turned fourteen on the same day, a full six months before the war broke out abroad. The ground was hard, the lake was freezing, and man who raised him was trying in vain to claw his way back to the surface from where he'd fallen through the ice. It was the easiest thing in the world to hold him under. The cold even stopped cutting into this skin after a while.
When he finally ran for help, no one asked for questions about his limp, blue-tinged arm or how the crazy drunk had fallen through in the first place. They only wrapped him in blankets and put him to rest while the adults worked it out. They took his exhaustion for grief and in their willful ignorance taught him a lesson that would see him through into adulthood.
People who think themselves too important to look down, can trip over almost anything.