Try having an argument with someone who thinks that 1/3 cup is less than 1/4 cup. Because 3 is less than 4, right? Never mind the fact that a smaller number in the denominator makes for an overall larger number. And most people who think things like that don't know what a denominator is.
Oh, I forgot this tidbit. Try talking to someone who thinks 1 1/3 cup in a recipe means 1/3 of a cup one time. When you try to tell them it means one whole cup plus 1/3 cup, they will say, "Then why didn't it say that?"