From the point of ordinary men, enlightenment and ingorance are two separate things. Wise men who thoroughly realise mind-essence, know that they are the same nature. This sameness of nature, that is non-duality of nature, is what is called "true nature", neither decreases nor increases; it is undisturbed in an annoying situation, and is calm in samadhi. It is neither eternal, nor not-eternal... it is beyond existence and non-existence.

--Venerable Hui Neng