Is enlightenment "sudden" or "gradual"? It's a centuries-old debate in the Zen world (and in other realms of Buddhist practice, too). Zen's answer has always been "yes" and "yes" - for while the realization of insights may be in instants beyond time, the cultivation and realization (that is, making real) is done via practice instant by instant in life.
Kensho (seeing original nature) is necessary and vital to this path. Can such happen in an flash? Yes, but it usually ends up a flash in the pan - unless cultivated slowly, step by step, and made a part of one's life. Must enlightenment happen in an flash? No, for the Buddha's Truths can pierce our marrowless marrow slowly, step by step, with steady years of practice. In either case, arriving at "no beginning no end", or any other destination, is not the end of the trail, nor the beginning. [Click through for more, and to "sit-a-long" with today's video.]
Today's Sit-A-Long video follows. Remember: recording ends soon after the beginning bells; a sitting time of 20 to 35 minutes is recommended.
(Here is the interview with Joko Beck mentioned today.)