Chi Sau is the most important part of Wing Chun training. The purpose of Chi Sau is to develop your instinct and sensitivity to your opponent, so when he moves you can react straight away. However Chi Sau is not the same thing as fighting though it will help you to develop your fighting skill. Chi Sau is also not the same thing as sparring. How are they different and how does Chi Sau develop fighting skill?
When fighting or sparring there is always a winner and loser: if you are beaten in a fight or in sparring then you have lost. Chi Sau does not look at things in the same way. The purpose of Chi Sau is to learn why you were hit and how to hit your opponent. So as long as you learn, whether you get hit or hit your opponent, you never lose. Then you can treat Chi Sau like a game and stay relaxed. This is the most important thing in Chi Sau – to stay relaxed.
Most people will lose a fight because they panic. When you panic you cannot move as you would like to or react as quickly as you should. You panic because you are not used to being in that situation and stress and so cannot keep calm. You don’t even know what you are doing or what is happening. It does not matter whether you study martial arts or not, if you panic then there is a good chance you will lose, especially if your opponent remains calm.
So the question is how do you stop yourself panicking? The only way to stop is to get used to the situation so it is familiar to you. Its is like driving a car, when you have a lot of experience then if some one steps out in front of you, you can react quickly and stop, however, if you are a new driver, you might panic and not know what to do. So you have to gain experience. One way to do this is fight a lot, almost everyday. If you fight a lot then you will know what it is like and so be able to stay calm and relaxed. Then you can use whatever skill you have learned. However if you do this, then you have to pay a high price. Physically, you will become very damaged and injured and other areas of your life will also be affected badly. So in the end you might not even be able to carry on your training.
However, there is one other way in which you can train where you do not have to pay this high price and it will teach you how to keep relaxed. Of course the answer is Chi Sau. As mentioned earlier, the most important things in Chi Sau is to stay relaxed. After you have trained in Chi Sau for a long time, you can stay relaxed whatever your opponent does, and can also use all the skill you have studied. If you can do this then you have developed the fighting skill. Of course there is never any guarantee that you won’t panic, even if you fight a lot, you cannot guarantee that. All that remains is to make sure that when you strike it is strong enough. This is more easy to do. To make a tense person physically and mentally relax is very difficult and takes a long time.
This is why Chi Sau is so important. If your Chi Sau is good then your Wing Chun will be good and if your Wing Chun is good, then your fighting skill will also be good.
This article is based on a series of discussion with Grandmaster Ip Chun whilst he was teaching in the UK.
 Ip Chun, The Art of Sticking Hands, Qi Magazine no. 54, pp. 26 (Apr 2001)