"All the causes, all the conditions of satori are in the mind; they are merely waiting for the maturing. When the mind is ready for some reasons or others, a bird flies, or a bell rings, and you at once return to your original home; that is, you discover your now real self. From the very beginning nothing has been kept from you, all that you wished to see has been there all the time before you, it was yourself that closed the eye to the fact. Therefore, there is in Zen nothing to explain, nothing to teach, that will add to your knowledge. Unless it grows out of yourself no knowledge is really yours, it is only a borrowed plumage."
An introduction to Zen Buddhism
(This has just blown my mind. It makes so much sense and rings a bell with what I've experienced.)