There was once a university professor who visited with a Zen master to talk of Zen-related matters. As they talked, it became clear to the Zen master that the professor, often talking at great length, already deemed himself quite astute in the subjects of Buddhism and Zen.
After listening for a time, the Zen master offered tea. On acceptance, the Zen master left the room and came back with a teapot and cup.
As the professor again began talking from where he’d left off, the Zen master poured the professor’s tea. When it reached the brim of the cup, the Zen master continued pouring. Tea spilled down the side of the cup, all over the table, and even onto the floor.
“Whoa! Whoa!” shouted the professor. “What in the world are you doing? Can’t you see it’s full?”
“You are like this cup,” the Zen master said. “You are already so full that nothing more can get in. You came here requesting to discuss Zen. How can I show you what Zen is if you do not first empty your cup?”
The professor was stunned into silence.
“Please,” said the Zen master, “go away and come back when you are capable of receiving.”