Thirty spokes unite around one hub to make a wheel.
It is the presence of the empty space that gives the function of a vehicle.
Clay is molded into a vessel. It is the empty space that gives the function of a vessel.
Doors and windows are chisel out to make a room.
It is the empty space in the room that gives its function.
Therefore, something substantial can be beneficial.
While the emptiness of void is what can be utilized.
~ Lau Tzu, Tao Te Ching