zero and beyond

A seeker arrives at a zen master's home,hoping to learn zen.
The zen master serves him tea. He pours his visitor's cup full, and then keeps on pouring as if it's normal to do so. The seeker curiously watches the overflow until he no longer could restrain himself.
"It is overfull. No more will go in!"
"Like this cup," the master said, "you are full of your own opinions and speculations. How can I show you what Zen is unless you first empty your cup?"