Perhaps this was overheard at the Rock, Paper, Scissors tournament:
Now that I know you choose paper, I clearly cannot choose rock. But since I know that you will now choose paper, I can safely choose scissors to soundly best you. But I see that you are clever. You would know that I would choose scissors, because you knew that I know you have the disposition to choose paper. Therefore I clearly cannot choose scissors, because you would counter with the rock.
/stolen from fark.com/