Suppose the probability of intelligent life (per unit volume) is zero. Then it still might have happened somewhere, and wherever it happened, there we would be. (If you fire a point bullet at a target, the probability of hitting a particular point is zero, but you are bound to hit some point if you hit the target at all.) However, the current picture seems to be that the whole universe is effectively infinite (the distant parts of the *observable* universe are winking out, but we are winking out from their point of view, and they can see stuff that we can't). But now, suppose that the probability of intelligent life is nonzero but extremely small. Then there might be no hope of finding another example in the observable universe, but almost surely (i.e., with probability 1) it has happened infinitely often, and in one of the places where it has, there we are. We cannot expect to distinguish these possibilities.