The puzzle isn't why people aren't ready to be heroes - in fact it's more the other way, why so many people do in fact find the strength and independence to be heroes in those kind of situations.

But the other mystery is how it comes about that there are other seemingly ordinary people who, seemingly of their own volition, are ready to do unspeakable things to other human beings. And the Milgram experiment suggested that, at least in that time and place, such people were a majority.

And then you think of what happened in Ruanda a few years ago - no sophisticated Nazi murder bureaucracy, just neighbours authorised to kill neighbours of a different ethnic group, and promptly doing just that. And you wonder how safe any of us are from our neighbours or from ourselves, if that is really what human beings are like. (And then you think, yes, but even in that time and place there were those who did in fact turn out to be heroes, at the risk of, and even at the cost of, their lives.)