The crucialmomentof thefilmis where, Iadmit, I have aquibble: it is grippingand evenmoving when Harryrealiseswhathisdestinyis, and sets out to fulfil it.
It is an amazing conceit, but that, unfortunately, is more or less what it remains: a conceit, which, having taken half the film to get moving, then grows increasingly hard to grasp as a practical enterprise, and even harder to believe in.