Zen Koan

My branch of Buddhism, Zen, deals mainly with two things: zazen and koans. My specific branch, Soto Zen, is mostly concerned with zazen. I never pay much attention to Buddhist koans and stories, however, this one is one of my favorite:

Nan-in, a Japanese master during the Meiji era (1868-1912), received a university professor who came to inquire about Zen.

Nan-in served tea. He poured his visitor's cup full, and then kept on pouring.

The professor watched the overflow until he no longer could restrain himself. "It is overfull. No more will go in!"

"Like this cup," Nan-in said, "you are full of your own opinions and speculations. How can I show you Zen unless you first empty your cup?"

This thought had a profound impact on me, especially since I've seen many examples of having to "unlearn" in real life.