[Sometimes] on examination it will be found that the "non-existent," the "void," "non-being," etc., of which so much has been written and taught...in fact represents nothing whatever but a philosopher's attempt to objectify subjectivity.
However, [trying] to conceive them as objects is simply looking in the wrong direction...these so familiar emptinesses are not objects at all, for they are what the perceiver of them is. He has reached a dead-end in his analysis and finds himself face to face with his own nature. But instead of recognising it as such and realizing that his void is "what an eye sees when it looks at itself," he goes on trying to objectify what he can never see by turning it into an objective concept.
[Fortunately] there has always been an alternative when the dead-end of conceptualization has been reached, and that is just to turn round and wake up to the truth. Having arrived at the gate [our philosopher] tried to prise it open, not realizing that he was already on the right side of it.
The traveller has only to turn round in order to find that he is already at his destination, which is home. The sought is then seen to be the seeker.
---Wei Wu Wei on the Heart Sutra