How do you know the fishes are enjoying themselves? (idea)

Taoist Mondo
One day Chuang-tzu and a friend were walking along a riverbank.
"How delightfully the fishes are enjoying themselves in the water!" Chuang-tzu exclaimed.
"You are not a fish," his friend said. "How do you know whether or not the fishes are enjoying themselves?"
"You are not me," Chuang-tzu said. "How do you know that I do not know that the fishes are enjoying themselves?"