For a wing chun teacher it is incumbent upon them to be able to explain, demonstrate and dissect all of the movements of the forms. There are many teachers out there who will talk for hours about the method, other who will smash their students with raw power, whilst some just elude to great force without ever showing it. It is easy to mask your failing with speed during a demo, but can they do it slow? As a student do you actually feel free to ask questions? Has your teacher freely broken down all of the movements, shown you how they work and why they do not work for you?
I have uploaded a great many videos to youtube of Chu Shong Tin teaching wing chun, for the reason that he not only talked the talk but walked the walk. He would let anyone, be they a visitor off the street or senior student, take his hand and feel how he generated power. There was no secret technique off limits to outsiders, no discrimination to lower grades, just a desire to give others an understanding. This really is not easy and takes great confidence. How did he know it would ALWAYS work? I guess that at first he didn't. Maybe for several years he failed every now and then; everyone does. But being a teacher is to be human and open yourself to vulnerability. The teacher would hides behind secrecy is the one who is masking his insecurity. I know students of 10 years experience who have not been shown the bill jee. Why? It is not as if they will steal it and use it to commit crime. If the fundamentals are not there to back it up it is no more dangerous than waving your arms around. Shame on the teacher who will not teach.
I say test your teacher, ask them questions, grill them and get them you to show you how they do it. They might fail, they might get it wrong, but if they are good they will rise to the challenge and keep improving. A really good teacher, someone worth following, is one who can not only do it themselves but someone who have the patience and sensitivity to pass the ability onto you. And when I say YOU, I do not just mean only the students who flatter their ego.
If your student-teacher relationship is just about money, buying a service, just walk away as neither of you is capable of achieving anything worthwhile. A proper teacher has already put in their time for the love of the art, there is no better use of their time than being with a student who is doing the same. If they show you the respect to put the time into you whilst in class, and you match that by practicing at home, great things are possible. Also remember that the class is the place where you get your homework marked, so sitting on the sofa between classes instead of practicing will not get you much more than a fat backside.
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