the first link in the chain of causality/dependent origination is ''ignorance''. when the nature of things is seen then ignorance is no longer possible and so the chain of causality begins to disintegrate. clinging and craving are no longer relevant if ignorance has ceased; they come further down the chain, before ''birth''.
if it is seen that Mind is emptiness then it is known that there is no one to be born, since Mind is all things (just about). when there is no mind there has been a cessation of the within, or own nature. it is no longer possible to look within and therefore the dharma eye closes.
enlightenement in Chan seems to be found in the saying of Huineng... ''see your nature and become a buddha''. the Nature of Mind or Emptiness. Before the oneness of Mind can be seen there needs to be a renunciation of all things, all names and all forms, through a vow.
when emptiness is seen, it is just this ordinary ''mind'' seeing daily things in an ordinary way. if you seek emptiness in the ordinary you will find it. the only way i know of that enables seeing emptiness is to see the nature within yourself. Some have called this emptiness, others mind, it is such as it is, suchness. just so.
perhaps the most accurate designation of nature is that it is just so. all things are just so. suchness.
so, if you wish to see Mind, emptiness or suchness then see your nature within. this ordinary nature is hard to see if you have an ego mind still clinging.
its so hard to talk about these things, they are very elusive. if someone keeps banging on about... see emptiness, or seeing Mind it is because the experience defies elaboration, and tends to be spoken about in simple terms only. simple though completely inacessible like a thousand foot iron wall. impenetrable.
hope this is helpful. if you wish to seen nature you must be creative and use all skillful means at your disposal. kind deeds, kind heart, kind mind, various forms of meditation, philosophical insight, creative exploration of different methods and means. its not impossible. the most precious commodity is time, to have time to search.
you can undergo all initiations you need through prayers to the buddhas and learned masters, you may even learn to speak directly to them after some practice.
sudden? is it, i dont know. it can happen in one lifetime with practice of skillful means, but how many lives have prepared one for this 'sudden' enlightenment. i dont know, perhaps very very many.
best wishes, Tom.
i am not a learned scholar, but am trying to speak of experience. i dont know whether this will be helpful or not. i hope it will. bless you.
in any matters of importance. dont rely on me. i may not know what i am talking about. take what i say as mere speculation. i am not ordained. nor do i have a formal training. i do believe though that if i am wrong on any point. there are those on this site who i hope will quickly point out my mistakes.