Often I see this lovely story reproduced. It goes something like this:
Two monks walk beside a river. One turns to the other and says,
See how the fish play! They are really enjoying themselves!
The second monk replies, You are not a fish!
How can you know that they are really enjoying themselves?
And the first retorts, You are not me!
How can you know that I do not know
that they are really enjoying themselves?
And the narrative ends and I think to myself MY WHAT A LOVELY STORY
ABOUT MONKS, WATER, FISH, PERCEPTION, AND REALITY. I GUESS
WE CAN'T REALLY EVER KNOW WHAT OTHER PEOPLE KNOW
BECAUSE WE AREn't them. It's true sort of!
The secret is that the story continues.
In my Zhuangzi (Columbia University Press. Translated by Burton Watson.)
the second monk exclaims, (and I am paraphrasing)
Yeah! But you're no fish! You still can't know
whether the fish really enjoy themselves!
and the first gets red in the face and gets all serious
Go back to your first question, please!
You said "How can you know" so you assumed I knew
that the fish were really enjoying themselves!
I'll tell you how. We are next to the river.
This is awkward which is why everyone omits it.
The first monk shouldn't have said "You are not me!" at all,
and should have answered the question the first time it was asked.
If you ask me, the story should go like this:
Two monks walk
beside a river.