The sound of one hand
Two hands clap and there is a sound. What is the sound of one hand?
— Hakuin Ekaku
"...in the beginning a monk first thinks a kōan is an inert object upon which to focus attention; after a long period of consecutive repetition, one realizes that the kōan is also a dynamic activity, the very activity of seeking an answer to the kōan. The kōan is both the object being sought and the relentless seeking itself. In a kōan, the self sees the self not directly but under the guise of the kōan...When one realizes ("makes real") this identity, then two hands have become one. The practitioner becomes the kōan that he or she is trying to understand. That is the sound of one hand." — G. Victor Sogen Hori, Translating the Zen Phrase Book