One day, a philosopher went to visit Master Nan-in to discuss zen with him. During the discussion, the philosopher would ask questions and as Nan-in began to answer, the philosopher would butt in with another question or would start sharing his own insights.
After this happened for two or three times, Nan-in took the teapot and started pouring tea into the philosopher’s cup (which was still full because he had kept talking).
The cup overflowed and the tea started spilling on the table and onto the floor.
The philosopher jumped up and said, “Stop it! The cup can take no more tea.”
Nan-in promptly stopped pouring and looked at the philosopher squarely. “The cup can take no more tea because it is full. Your head can take nothing from me because it is full of your own ideas.”
“If you would learn from me, sir, please empty your cup first.”