Why we can't imagine the moment of our death

Thumbing through a recent issue of The New Yorker last night, I came across a thought-provoking paragraph about mortality in a "personal history" piece by Aleksandar Hemon.

There's a psychological mechanism, I've come to believe, that prevents most of us from imagining the moment of our own death. For if it were possible to imagine fully that instant of passing from consciousness to nonexistence, with all the attendant fear and humiliation of absolute helplessness, it would be very hard to live. It would be unbearably obvious that death is inscribed in everything that constitutes life, that any moment of your existence may be only a breath away from being the last. We would be continuously devastated by the magnitude of that inescapable fact. Still, as we mature into our mortality, we begin to gingerly dip our horror-tingling toes into the void, hoping that the mind will somehow ease itself into dying, that God or some other soothing opiate will remain available as we venture into the darkness of non-being.