Your instructor has just demonstrated a new exercise. He explained in detail what the purpose of the exercise is, how you should train it, he even showed it in slow motion for the finer points. Maybe on top you were told what not to do, in order to ensure your progress.
I for example often encourage to train it a few times purposely wrong. Only if we know common mistakes we can go into the right direction. I ask not to hinder each other, rather to help each other, even though that would seem to be the most normal thing in the world. I urge not to fight each other, since each training partner first has to get a feel for the exercise.
When I show an exercise in different angles, with different outcomes, I point out that this is a "finished product", a ability to move, strike, counter, etc. that has to be achieved first.
Furthermore differences in height, reach, experience, weight, strength, speed, even personality can heavily influence the outcome of a exercise. Training partners have to work WITH each other, to eventually after long training reach a level of intensity at which they can test "the finished" exercise against each other.
But even after ideal explanations and demonstrations what happens at times? You just get started with your training partner, and ... ??? he starts to point out that your Wu-Sau was too low, that you should have turned earlier, that your punch didn't perform according to the distance, and the list goes on.
You start thinking, hey just wait a minute, you are doing the very same things, besides we have just started to explore the exercise, and if I remember right haven't you missed quite a few classes recently, and all you do is trying to correct me?
Does this scenario seem familiar? Maybe if you have never encountered it, you should nicely ask your training partner? Maybe he will start talking ... :-)
Having experienced this behaviour everywhere, I know it is human nature, the I-know-it-better effect.
Just a short while ago I read a very interesting article on the web site of the EWTO. "When correction is a disturbing factor" Why it is not good to constantly correct your training partner, and why it is also bad to give a running commentary during a lesson. Grandmaster Kernspecht and guest author Sifu Lars Böckers on “bad habits“ during WT training.
Find it here: http://www.wingtsunwelt.com/news.php?id=1315