Tao Te Ching Chapter 11
Thirty spokes unite around the nave;
From their not-being (loss of their individuality)
Arises the utility of the wheel.
Mold clay into a vessel;
From its not-being (in the vessel's hollow)
Arises the utility of the vessel.
Cut out doors and windows in the house (-wall),
From their not-being (empty space) arises the utility of the house.
Therefore by the existence of things we profit.
And by the non-existence of things we are served.