The main objective of Wing Tsun is to be a realistic system of self-defense. Wing Tsun does not focus on fighting “techniques”, instead relying on fighting and energy principles to be followed at all times. The central idea is that, under pressure, it is impossible to visually recognize the precise direction and speed of an attack and make a conscious decision on an effective way in which to react, all within the very brief amount of time you have before your opponent's attack lands. Rather, one must (counter) attack immediately in a very direct and protected manner and rely on reflexes to determine how to react if the opponent's attack continues to pose a problem

http://en.wikipedia.org/wiki/Wing_Tsun