A comparison between defending yourself and attacking:

Reaction time + Blocking time = overall defence time   0.745 secs      + 0.15 secs       =   0.895 secs

 

If, as an example, we compare this overall defence time of roughly 0.9 seconds with the time a skilled fighter requires to land a central straightline punch at close quarters (approx 0.15 to 0.2 seconds), then you will agree that a successful and systematic defence is nearly impossible if traditional methods are applied.

 

So in Wing Tsun we use something called Aggressive Defence. This means that instead of using the traditional block we will defend and attack at the same time with a punch.

I am not trying to say that you should be the first to attack but as soon as you know he is going to attack you (i.e. clenched fists or shift of body weight), then you should go in with a move i.e. the straighline punch.

Most of the realistically inclined, top-class representitives of traditional styles are at least subconsciously aware of this defensive weakness. This is why you will hardly ever see a single specific block in full-contact competitions.