Thirty spokes share the wheels hub;
It is the centre hole that makes it useful.
Shape clay into a vessel;
It is the space within that makes it useful.
Cut doors and windows for a room;
It is the holes which make it useful.
Therefore profit comes from what is there;
Usefulness from what is not there.
 Lau says:
Thus, what we gain is Something, but it is by virtue of
Nothing that it can be put to use'.
The Ma wang tui has:
'Therefore, we regard having something as beneficial,
But having nothing as useful'.
Cheng's commentary is interesting. After going on about the emptiness as the useful, etc., he says: '... that which is there is a mere advantage. According to the following chapter, the Sage concerns himself with the abdomen and not with the eyes. 'Reinforcing the abdomen' mean ch'i (breath); 'fill the valley' also means ch'i. Hence the abdomen ought to be as empty as the valley, just as the valley is as full (reinforced) as the abdomen. If one can achieve this, once gets both advantage and usefulness. If the eyes aggressivekly look outward, the spirit will suffer harm. If one can allow the spirit to exist unobtrusively and cultivate the breath (ch'i) as if one had no eyes, one can also add 'usefulness' to the 'advantage' of eyes.'
In the Chuang-tze there is the tale of the Emperor going to visit his kitchens and watching a butcher cup up an ox. Let me see if I can find it... Here (for all I much prefer Gia-fu Zengs version) ia version by Burton Watson. Just thought it might be an idea to change sources:
Cook Ting was cutting up an ox for Lord Wen-hui. At every touc of his hand, every heave of his shoulder, every move or his feet, every thrust of his knee - zip! zoop! He slithered the knife along with a zing and all was in perfect rhythm as though he were performing the Dance of the Mulberry Grove or keeping time to the Ching-shou music.
"Ah this is marvellous!" said Lord Wen-hui. "Imagine skill reaching such heights!"
Cook Ting laid down his knife and replied, "What I care about is the Way, which goes beyond skill. When I first began cutting up oxen, all I could see was the ox itself. After three years I no longer saw the whole ox. And now - now I go at it by spirit and don't look with my eyes. Perception and understanding have come to a stop and spirit moves where it wants. I go along with the natural makeup, strike in the big hollows, guide the knife through the big openings, and follow things as they are. So I never touch the smallest ligament or tendon, and much less a main joint.
"A good cook changes his knife once a year - because he cuts. A mediocre cook changes his knife once a month - because he hacks. I've had this knife of mine for nineteen years and cut up thousand of oxen with it, and yet the blade is as good as if it had just come from the grindstone. There are spaces between the joints, and the blade of the knife as really no thickness. If you insert what has no thickness into such spaces, then there's plenty of room - more than enough for a blade to play around in. That's why after nineteen years the blade of my knife is still as good as when it first came from the grindstone.
"However, whenever I come to a complicated place, I size up the difficulties, tell myself to watch out and be careful, keep my eyes on what I'm doing, work very slowly and move the knife with the greatest subtlety, until - flop! the whole thing comes apart like a clod of earth crumbling to the ground. I stand there holding the knife and look all around me, completely satisfied and reluctant to move on, and then I wipe off the knife and put it away."
"Excellent!" said Lord Wen-hui. "I have heard the words of Cook Ting and learned how to care for life!"
Confucius (who was a master of the Chinese table lue known as the ch'in - one of my two favourite instruments) had this to say to the grand music-master of Lü on the playing of music (Legge's translation): 'How to play music may be known. At the commencement of the piece, all the parts should sound together. As it proceeds, theyshould be in harmony while severally distinct and flowing without break, and thus on to the conclusion.'
I tried to explain this to a young guitar student once: he thought I was trying to make a fool of him and never came back. Subsequently, he has become an extremely competent and utterly vacuous 'guitar hero'. An 'entertainer'. Pity...
[I hope you'll accept my apparently 'elitist' distinction between an 'artist' and an 'entertainer'?... Tous les Matins du Monde - the battle between the view of art of the Sieur de Saint Colombe (who played and composed only for the ghost of his dead wife) and Marin Marais (who wanted to be a pop star at the court of the kings), a tale which (since I have had much to do with - or, rather, against/despite - the music "industry") is very close to my heart - is about just this.]