"Empty your cup" is an old Chinese Chan (Zen) saying that occasionally pops up in western popular entertainment. "Empty your cup" often is attributed to a famous conversation between the scholar Tokusan (also called Te-shan Hsuan-chien, 782-865) and Zen Master Ryutan (Lung-t'an Ch'ung-hsin or Longtan Chongxin, 760-840).
Scholar Tokusan, who was full full of knowledge and opinions about the dharma, came to Ryutan and asked about Zen. At one point Ryutan re-filled his guest's teacup, but did not stop pouring when the cup was full. Tea spilled out and ran over the table. "Stop! The cup is full!" said Tokusan.
"Exactly," said Master Ryutan. "You are like this cup; you are full of ideas. You come and ask for teaching, but your cup is full; I can't put anything in. Before I can teach you, you'll have to empty your cup."
This is harder than you might realize. By the time we reach adulthood we are so full of, um, stuff that we don't even notice it's there. We might consider ourselves to be open minded, but in fact everything we learn is filtered through many assumptions and then classified to fit into the knowledge we already possess.
The Buddha taught that conceptual thinking is a function of the Third Skandha. This skandha is called Samjna in Sanskrit, which means "knowledge that links together." Unconsciously, we "learn" something new by first linking it to something we already know. Most of the time, this is useful; it helps us navigate through the phenomenal world.
But sometimes this system fails. What if the new thing is utterly unrelated to anything you already know? What usually happens is misunderstanding. We see this when westerners, including scholars, try to understand Buddhism by stuffing it into some western conceptual box. That creates a lot of conceptual distortion; people end up with a version of Buddhism in their heads that is unrecognizable to most Buddhists. And the whole is Buddhism philosophy or religion? argument is being perpetrated by people who can't think outside the box.
To one extent or another most of us go about demanding that reality conform to our ideas, rather than the other way around. Mindfulness practice is an excellent way to stop doing that, or at least learn to recognize that's what we're doing, which is a start.
But then there are ideologues and dogmatists. I've come to see ideology of any sort as a kind of interface to reality that provides a pre-formed explanation for why things are as they are. People with faith in ideology may find these explanations very satisfying, and sometimes they might even be relatively true. Unfortunately, a true ideologue rarely recognizes a situation in which his beloved assumptions to not apply, which can lead him into colossal blunders.
But there is no cup so full as that of the religious dogmatist. I read this today at Brad Warner's place, about a woman friend to interviewed a young Hare Krishna devotee.
"Turns out her Hare Krishna friend told her that women are naturally submissive and their position on earth is to serve men. When Darrah tried to counter this assertion by citing her own real-life experience, her buddy literally went "Blah-blah-blah" and proceeded to talk over her. When Darrah finally managed to ask how he knew all this, the Hare Krishna pointed to a bookshelf and said, 'I have five thousand years of yogic literature that proves it's true.'"
This young man is now dead to reality, or reality about women, at least.