Chuang Tzu and Hui Tzu had strolled on to the bridge of the Hao, when the former observed, “See how the minnows are darting about! That is the pleasure of
fishes.” “You not being a fish yourself,” said Hui Tzu, “how can you possibly know in what consists the pleasure of fishes?” “And you not being I,” retorted Chuang Tzu, “how can you know that I do not know?” “If I, not being you, cannot know what you know,” urged Chuang Tzu, “it follows that you, not being a fish, cannot know in what consists the pleasure of fishes.” “Let us go back,” said Chuang Tzu, “to your original question. You asked me how I knew in what consists the pleasure of fishes. Your very question shows that you knew I knew. I knew it from my own feelings on the bridge.”
Quote cut from a paper by William Buckingham given here It is interesting to read what the paper has to say further.