[According] to Ikkyu Sojun (1394 - 1481), . . . in his philosophy of "red thread zen," sex deepened the experience of enlightenment. No one can enter this world without being born of both a man and a woman, he said; we are connected to sex by the "red thread" of blood at birth. Back and back the red thread goes, long and unbroken, to the origin of all being. We're of sex. The fact should be embraced, not avoided.
— Philip Toshio Sudo, Zen Sex