In the Chapter Introduction, “The Immature and the Wise,” to The Dhammapada (trans. and ed. Eknath Easwaran), S. Ruppenthal very parsimoniously and elegantly describes the Zen view of “sudden awakening/gradual cultivation”:

In Buddhism, enlightenment (sambodhi or bodhi) is an instantaneous experience in which mental activity is momentarily suspended completely and sleeping realms of consciousness are dazzled into full wakefulness. Bodhi is not nirvana. It is a temporary stilling of the mine, which brings illumination of consciousness; nirvana, the permanent release from all sources of suffering, is attained only when the experience of enlightenment has been repeated so often that it, not ordinary conditioned awareness, has become one’s constant state. Only when the insights of bodhi are completely absorbed into one’s character and conduct would the Buddha call a person truly awake. (pp. 121-2)

While I don’t have time to comment on this so very clear exposition, I’d like, all the same, to give special thanks to my wife Alexandra and to my conversation partner Daniel for having discussed “sudden awakening/gradual cultivation” with me.