Nan-in served tea.
While the master quietly served tea, the professor talked about Zen.
The master poured the visitor’s cup to the brim, and then kept 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?”
Our ego-identities are barriers to deeper knowledge. They prevent us from imbibing new thoughts as these have to struggle past deeply entrenched ideas associated with our ego-self. Till we empty our cup off these we shall be unable to grasp the deeper essence of Zen. Yoga is a journey of slowly draining this cup and moving out of our ego-identity.