One day, a scholar went to see a Zen monk named Nanin to inquire about Zen. Nanin treated his guest to a cup of tea.
He poured the tea into a cup, and when the cup was full, he kept right on pouring.
The scholar said:"Master, that's enough! It's full!"
"You are just like this cup--full of your own thoughts and ideas. If you don't first empty yourself, how can I teach you about Zen?" said the Master.
If your mind is filled with your own prejudices, the truth that others speak can't be heard. When engaging in conversation, most people are in a hurry to express their own opinion, and as a result, they don't hear anything but the sound their own voice.(From Zen Stories: The Staff and Shout of the Venerable Ones)