Knowing Fish

One day Chuang Tzu and a friend were walking by a river. "Look at the fish
swimming about," said Chuang Tzu, "They are really enjoying themselves."
"You are not a fish," replied the friend, "So you can't truly know that they
are enjoying themselves."

"You are not me," said Chuang Tzu. "So how do you know that I do not
know that the fish are enjoying themselves?"