One day Chuang Tzu and a friend were walking by a river.
“Look at the fish swimming about. They are really enjoying themselves.” said Chuang Tzu
“You are not a fish. So you can’t truly know that they are enjoying themselves.” replied his friend.
“You are not me,” said Chuang Tzu.
“So how do you know that I do not know that the fish are enjoying themselves?”