"In observing Rabbi Yosef Zundel one day, Reb Yisrael slipped on a twig, or some such. He attracted Rabbi Zundel's attention. There followed one of the great moments in Jewish spiritual history.
Here was a young boy, secretly observing his ideal. Here was a ripened scholar and pietist, discovering he was being followed. The scholar had to respond to the moment - to a boy's yearning, to an opportunity to turn a moment of embarrassment into a lesson of the spirit.
Rabbi Yosef Zundel rose to the occassion, for his humility before Hashem included certainty about the way to it. He turned to the fledgling disciple, read the question on his face, told him how to proceed:
'Yisrael! Study mussar, that you may become one who fears heaven!'
They transformed Reb Yisrael. They entered his heart 'as a flaming arrow' (as he later put it). They constituted the prescription for the spiritual ascent to which he aspired, the ascent he had witnessed in Rabbi Yosef Zundel."
-The Fire Within, pp. 40-41, by Rabbi Hillel Goldberg