Thirty spokes share one hub. Adapt the nothing therein to the purpose in hand, and you will have the use of the cart. Knead clay in order to make a vessel. Adapt the nothing therein to the purpose in hand, and you will have the use of the vessel. Cut out doors and windows in order to make a room. Adapt the nothing therein to the purpose in hand, and you will have the use of the room. Thus what we gain is Something, yet it is by virtue of Nothing that this can be put to use.

Lao Tzu
Hughes, Patrick and George Brecht. Vicious Circles and Infinity: A Panoply of Paradoxes.