Euclid that is a silly thing to say. If you go down to a small enough scale nothing is perfectly flat and there is space between the particles/atoms. For the purposes of the example we are trying to get the stone "perfectly" flat. You are trying to achieve flat on a similar level of "flatness" that you want to be exhibited in your razor. I will agree with you in saying you are trying to remove crap from between the grits though.