A learned man once went to visit a Zen teacher to inquire about Zen. As the Zen teacher talked the learned man frequently interrupted to express his own opinion about this or that.
Finally, the Zen teacher stopped talking and began to serve tea to the learned man. He poured the cup full, then kept pouring until the cup overflowed.
« Stop », said the learned man. « The cup is full, no more can be poured in. »
« Like this cup, you are full of your own opinions », replied the Zen teacher. « If you do not first empty the cup, how can you taste my cup of tea? ».

Dans la meme veine, un autre proverbe zen: « The usefulness of a cup is in its emptiness. »