Where does Chi Sao fit in?

I have been pondering what makes Wing Tsun (Wing Chun too) special.  In describing the Wing Tsun ideals to a prospective student I am often discussing how Wing Tsun trains using the force of its opponent against them, focuses on body structure and angles as well as simple effective tools (all true).  However, look at the marketing material of *insert your martial art here* and those same things are said.  I believe that each person teaching a martial art also believes that what they are saying is true as well.

From my own general interest I saw this as true when watching and reading about western boxing, traditional and modern karate, MMA, BJJ, etc.  I see instructors talking about the importance of using your body (to various degrees) to add to each strike - hey, that's what I talk about.

So while true and it is practiced uniquely in Wing Tsun, it is also practiced by every self defense regiment to some degree.

So what is unique to Wing Tsun (and Wing Chun)?

So far the skill set that is unique to Wing Tsun is sensitivity training.  The ability to have barely touched an opponent and know which direction their arm/leg is going and respond to it faster than eyes can track.  When done well, it is like a hot knife slicing through butter and I've seen it done (and had it done to me).  Wing Tsun calls this Chi Sao, translated as sticking/sticky hands.  Training this specific skill set, which differentiates Wing Tsun from other martial arts takes a significant portion of intermediate to advanced level training.  Looking at our curriculum, its the lion's share of student grade 5-11 though in my opinion a good instructor balances this (awesome) skill acquisition with application/progressive training against resistance.

Tai Chi/Push hands has some similarities but is not exactly the same.   I have also read of less well known Malaysian martial arts (referenced by Sifu K Kernspect in his Wing Chun Illustrated article in 4/2020) that use similar principles.

Why sensitivity training?  What makes it so special?  Like chi, it is better felt than written about.  When a force is redirected at its earliest stages of movement it is easiest to move.  How early one can feel this is dependent on how skilled one is at sensitivity training.  I do not jest when I say the ideal time to sense and re direct movement is before it has moved.

I don't mean to understate Wing Tsun as a complete fighting system (which it is) and its unique and well thought out fighting strategy and philosophy.  While I believe Wing Tsun is special in these regards I am sure that any devotee to *insert your martial art here* would say the same so I did not mention that.  It would be a worthwhile blog later.