Thirty spokes converge upon a single hub;
It is on the hole in the center that the use of the cart hinges.
We make a vessel from a lump of clay;
It is the empty space within the vessel that makes it useful.
We make doors and windows for a room;
But it is these empty spaces that make the room livable.
Thus, while the tangible has advantages, it is the intangible that makes it useful.