Clay is moulded to make a vessel, but the utility of the vessel lies in the space where there is nothing. . . . Thus, taking advantage of what is, we recognize the utility of what is not.
Nothing in the world is more flexible and yielding than water. Yet when it attacks the firm and the strong, none can withstand it, because they have no way to change it. So the flexible overcome the adamant, the yielding overcome the forceful. Everyone knows this, but no one can do it.