Nan-in, a Japenese master during the Meiji era (1868-1912), received a university professor who came to inquire about Zen.
Nan-in served tea. He poured his visitor’s cup full, and then kept on going.
The professor watched the overflow until he no longer could restrain himself. “It is overfull. No more will go in!”
“Like this cup,” Nan-in said, “you are full of your own opinions and speculations. How can I show you Zen unless you first empty your cup?”
From Zen Flesh, Zen Bones. Compiled by Paul Reps and Nyogen Senzaki. Published by Doubleday.