If we assume that we&#x27;re observing at a random point in our history, we are equally likely to be observing at a point in the first 10%, second 10%, third 10%, and so on.  That&#x27;s what the assumption means.  Which means there is a 10% chance that we&#x27;re observing in the last 10%.<p>See <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Doomsday_argument" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Doomsday_argument</a> for the most famous use of this line of argument.  (It concludes that the human species is likely not long for this universe.)