The reason that I likely drew ball number 7 from the ten ball urn rather than the million ball urn is that the million ball urn had a lot more balls that I could have drawn making it less likely for me to have selected a number less than 11. It works because the other 999,990 balls were available for drawing. If I could reach only balls 1 to 10 in either urn then drawing ball number 7 would tell me nothing about which urn I selected. Since people who haven't been born yet aren't available for drawing, the selection of me here and now tells us nothing about how many more people are likely to be born.