"Thirty spokes join together in the hub. It is because of what is not there that the cart is useful. Clay is formed into a vessel. It is because of its emptiness that the vessel is useful. Cut doors and windows to make a room. It is because of its emptiness that the room is useful. Therefore, what is present is used for profit. But it is in absence that there is usefulness."

The ancient masters have debated the meaning of this saying since time immemorial but it probably just means that it's ok that you're stupid.