From The Song of the BIrd

No Zen student would presume to teach others until he had lived with his master for at least ten years.

Tenno, having completed his fen years of apprentiship, acquired the rank of teacher. One day he went to visit the master Nan-in. It was a rainy day, so Tenno wore wooden clogs and carried an umbrella.

When he walked in, Nan-in greeted him with ” You left your wooden clogs and umbrella on the porch, didn’t you? Tell me, did you place your umbrella on the right side of the clogs or on the left?”
Tenno was embarrassed, for he did not know the answer. He realized he lacked awareness. So he became Nan-ins student and labored far another fen years to acquire constant awareness.

The person who is ceaselessly aware: the person who is totally present at each moment: behold the master!