Thirty spokes will converge
In the hub of a wheel;
But the use of the cart
Will depend on the part 
Of the hub that is void.

With a wall all around
A clay bowl is moulded;
But the use of the bowl
Will depend on the part
Of the bowl that is void.

Cut out windows and doors
In the house as you build;
But the use of the house 
Will depend on the space
In the walls that is void.

So advantage is had
From whatever is there;
But usefulness arises
From whatever is not.

Tao Te Ching