Human beings know something terrible. We know that one day we're going to wake up, and it will be the last time we ever do. We know that one day will be the last day of our lives. We know, in short, that one day - inevitably, inexorably, inescapably - we're going to die. It is an unfortunate by-product of our intelligence that we are burdened with this knowledge, knowledge that no other animal on the planet could hope to possess. And it is, to use the technical term, a bit of a bummer.