The wise person dines on something more subtle: He eats the understanding that the named was born from the unnamed, that all being flows from non-being, that the describable world emanates from an indescribable source.
Once upon a time a man whose ax was missing suspected his neighbor's son. The boy walked like a thief, looked like a thief and spoke like a thief. But the man found his ax while digging in the valley, and the next time he saw his neighbor's son, the boy walked, looked and spoke like any other child.
Clay is fashioned into vessels; it is on their empty hollowness that their use depends. Doors and windows are cut out to make a dwelling, and on the empty space within, its use depends. Thus, while the existence of things may be good, it is the non-existence in them that makes them serviceable.