Stories remain in our consciousness, often unnoticed, as points of reference for understanding elements of life.However weird or enigmatic they are, or perhaps because of those very qualities, Zen stories have touched the hearts of people for over a thousand years.
One of the most frequently quoted Zen stories in the West seems to be one about a person who went to see a Zen master with a load of questions and arguments. The master kept pouring tea into a cup for the guest until it started overflowing. To the panicked guest , the master said,"If your mind is already filled like this, how can there be room for you to learn?" This seemingly unrealistic story was introduced in Paul Reps's Zen Flesh Zen Bones. Presenting a certain truth about learning, this story illustrates a paradox - the power of what might be called "positive emptiness".
Kazuaki Tanahashi (in Essential Zen)