A Zen master was relaxing in his yard when one of his friends, a professor from the university, stopped in for a visit.
"I want to study Zen buddhism" — he told him.
The master served tea.
He poured his visitor’s cup full. But continued pouring.
The professor watched the cup overflow. He watched the tea spill all over the table until he could no longer restrain himself.
“It's full! There's no room for more tea in my cup!”
“Like this cup,” the master said, “you are full of your own opinions and speculations. How can I show you Zen unless you first empty your cup?”