And if joy were not on the earth,
There were an end of change and birth,
And Earth and Heaven and Hell would die,
And in some gloomy barrow lie
Folded like a frozen fly.
Thirty spokes meet in the hub. Where a wheel isn't is where it's useful. Hollowed out, clay makes a pot. Where the pots not is where it's useful. Cut doors and windows to make a room. Where the room isn't, there's room for you. So the profit in what is, is in the use of what isn't.