Thirty spokes unite in one hub;

It is precisely where there is nothing, that we find the usefulness of the wheel.

We fire clay and make vessels;

It is precisely where there’s no substance, that we find the usefulness of clay pots.

We chisel out doors and windows;

It is precisely in these empty spaces, that we find the usefulness of the room.

Therefore, we regard having something beneficial;

But having nothing as useful.

–The Tao Te Chin (Chap. 11)