From the Tao Te Ching

11. Thirty spokes are united around the hub of a wheel, but the usefulness of the wheel depends on the space where nothing exists. Clay is molded into a vessel, but the usefulness of the vessel depends on the space where nothing exists. Doors and windows are cut out of the walls of a house, and the usefulness of the house depends on the space where nothing exists. Therefore take advantage of what exists, and use what does not exist.

76. When people are born, they are tender and supple. At death they are stiff and hard. All things, like plants and trees, are tender and pliant while alive. At death they are dried and withered. Therefore the stiff and hard are companions of death. The tender and supple are companions of life. Thus strong arms do not win. A stiff tree will break. The hard and strong will fall. The tender and supple will rise.