A learned man once went to a Zen teacher to inquire about Zen. As the Zen teacher explained, the learned man would frequently interrupt him with remarks like, "Oh, yes, we have that too...." and so on.

Finally the Zen teacher stopped talking and began to serve tea to the learned man. He poured the cup full, and then kept pouring until the cup overflowed.

"Enough!" the learned man once more interrupted. "No more can go into the cup!"

"Indeed, I see," answered the Zen teacher. "If you do not first empty the cup, how can you taste my cup of tea?"