Harry is one of those people you see rarely in reality and often in fiction: the kind that "break stronger."

That is to say, when faced with a crisis they cannot handle, they become more dedicated, more single-minded, to the point of obsession.

It makes them very very dangerous people, up until the moment their goals are either achieved or made impossible, at which point they (lacking anything else to base their lives around) crumble into so much dust.