The Ever Unnameable It – Talk by Ron Sinnige (pdf).
"A man up a tree who hangs from a branch by his mouth is asked by another man under the tree the essence of Zen. If he answers, he will fall from the tree and die. If he does not answer, he cannot meet the need of the questioner. How can he break through the barrier of this great dilemma? Unless one faces the inescapable crisis and has once had the experience of dying, one will not have true freedom."
Zenkei Shibayama, The Gateless Barrier