Why does this not surprise him? It's almost as though he expected this, a moment of serious deja vu overcoming Childermass for a moment there. As such, he only stares at first, giving Strange the look he likely anticipated, like he's a lunatic, which, franky—

"Then you're already there," he finally says, "You were always a terrible man," which doesn't sound right, something making that difficult to say to the mage, "And now you're an insane one, too, and for what? You're miserable."