Nan-in, a Japanese master during the Meiji era, welcomed into his home a university professor who had asked to see him. The professor arrived, answered the master's simple, polite greeting with a brusque, arrogant reply, and strode past him into the house. The old man followed his guest quietly into the sparsely furnished living space and watched, his customary peaceful expression undisturbed, as the professor seated himself without being asked.
"Will you honor me as my guest for tea?" Nan-in asked the professor.
"Yes, I'd like tea," was the blunt reply. "And I want to ask you some questions," the professor continued with a self-satisfied smirk. "They say you are very wise, and I would learn what you have to teach."
"Certainly," Nan-in replied. "I will gladly share all I know. But first, let us have tea."
The professor frowned at Nan-in, then sighed impatiently. "Very well," he said, his voice curt. He rearranged his silken coat. "After tea."
Nan-in focused on his task. He prepared the tea to the perfect temperature, steeped it just long enough but not too long, and set the simple, lovely dishes in an orderly arrangement on the cloth. The professor cleared his throat and adjusted his coat again. Nan-in at last finished all his preparations and was ready to pour.
The master held the pot over his visitor's cup and began to serve him tea. The professor impatiently reached for the cup before it was half-full, but Nan-in continued filling the cup. He poured his visitor's cup three-quarters full and then kept on pouring. When the cup was full to the brim, Nan-in kept pouring, and the tea ran over the edge of the cup into the saucer. Nan-in, gazing calmly at the cup, continued to pour, and the tea overran the saucer and began to run over the table.
The professor watched the overflow until he could no longer restrain himself. "The cup is full. No more will go in!"
"So it is," said Nan-in contentedly, and he stopped pouring tea into the cup. He looked at the professor with his kind, steady gaze, and said, "Like this cup, you are full to the brim with your own opinions, your own importance. How can you learn anything unless you first empty your cup?"