A university professor approached a master hoping to learn about the nature of Zen.  “I know a great deal about the workings of the physical world,” the scholar explained, “but perhaps you could add to my knowledge by offering me thoughts about the nature of the spiritual world.

“Let us have a cup of tea,” said the master, “and then we shall talk.”  The professor held out his cup as the master poured, filling the cup to the brim and then continuing to pour while the tea spilled onto the floor.

“It is overflowing!” protested the professor.  “No  more will go in!”

“Yes, it is so,” said the master.  “Just as this cup is full to overflowing, so is your mind filled with opinions and speculations, leaving no room to receive the teachings.  Only when you empty your cup can we begin.”