"Thirty spokes meet the hub but it is the emptiness between them that makes the essence of the wheel. From clay pots are made, but it is the emptiness inside them that makes the essence of the pot. Walls with windows and doors form the house, but it is the emptiness between them that makes the essence of the house. The principle: The material contains usefulness, the immaterial imparts essence."

- from the eleventh aphorism of Lao-Tse (via vvissen)