Verse 11

Wu is nothingness, emptiness, non-existence

Thirty spokes of a wheel all join at a common hub
    yet only the hole at the centre
    allows the wheel to spin
Clay is moulded to form a cup
    yet only the space within
    allows the cup to hold to hold water
Walls are joined to make a room
    yet only by cutting out a door and a window
    can one enter the room and live there

Thus, when a thing has existence alone
    it is mere dead-weight
Only when it has wu, does it have life