A philosopher asked a Zen Master to explain Zen to him in as few words as possible.
The Zen Master started pouring some tea to a cup. The cup filled up quickly, but the Zen Master kept pouring.
"What you are doing makes no sense," objected the philosopher. "The cup is full. You cannot pour any more tea into it unless you first empty it."
"So it is with your mind," said the Zen Master. "It is filled with ideas and conceptions. I cannot teach you Zen until you empty your mind."