Joined: Oct. 2007
hmmm... you could talk about insurance companies? An insurance company can accurately predict how many of its customers are likely to break their legs in any given year, but they can't even begin to predict which ones those customers will be.
Alternately, you could talk about radioactive decay. Given a chunk of Radioactive Element X with [number] atoms of Element X in it, you can make very accurate predictions about the quantity of atoms that will decay in any given time period, but even in principle, there's no way to tell in advance *which* of those atoms will decay.