Clay is fashioned into vessels; it is on their empty hollowness that their use depends. Doors and windows are cut out to make a dwelling, and on the empty space within, its use depends. Thus, while the existence of things may be good, it is the non-existence in them that makes them serviceable.
The best people are like water, which benefits all things and does not compete with them. It stays in lowly places that others reject. This is why it is so similar to the Way.