A simpler variation goes as follows: at "t" = 0, there is one marble in the jar with the number 0 scribbled on it. At "t" = 0.5, the number 0 on the marble gets replaced with the number 1, at "t" = 0.75, the number gets changed to 2, etc. Now, no marbles are ever added to or removed from the jar, so at t = "1", there should still be exactly that one marble in the jar. However, since we always replaced the number on that marble with some other number, it should have some number "n" on it, and that is impossible because we know precisely when that number was replaced, and never repeated again later. In other words, we can also reason that no marble can be left at the end of this process, which is quite a paradox.