Great faith. Great doubt. Great effort. The three qualities necessary for training. From The Little Book of Zen

For the study of Zen, there are three necessities: the great root of faith, the great ball of doubt, and the great strength of tenacity. From “Bobo the Priest,” in Zen Inklings, by Donald Richie

There are three factors for success in the study of Zen; great faith, great resolution and great spirit of inquiry. T’ui-yin, 1579