…are “I know that”.
The brain is a computer, and words are code. The way the brain responds to this particular command is by shutting down new knowledge acquisition, since its resources are finite and knowledge assimilation takes energy. This happens if you even think these words silently to yourself, but if you really want to halt your learning progress, as well as annoy your teacher, say them out loud, because that gives them even more power.
Anyone who has been around martial arts schools for a while has seen it happen: someone with previous experience comes into a new school, and the whole time they are training they keep saying “In my old style we did it this way…” News flash: not only are you shooting your progress in the foot, you are also annoying everyone else in the room. Suggestion: don’t be that guy. Instead, if you go to a new school, even if you have a 10th degree black belt in your previous system, be like Jon Snow and pretend that you know nothing (which is how a true high level master would behave anyway). This has always been my policy when going to a new school (and I have been to many), and it should be yours as well.
When I began learning tai chi I already had twelve years of (external) martial arts experience, but I didn’t try to bring it into class with me, because I realized that I was learning something different than I had learned before. I also had a sifu who said certain things over and over again, such as “step light, arrive heavy”, “sink the shoulders”, and, of course, “relax”. It is because I heard these things repeatedly that they sunk in and stuck, not just cerebrally, but somatically. Repetition is a necessary part of the learning process. Remind your ego that it won’t hurt you to hear again something that you think you already know, and in fact it is actually good for you.
You’ll never impress your teacher by explaining how much you already know, but if you keep your mouth shut you might impress them by how quickly you acquire new skills. But that doesn’t matter anyway, because being impressive isn’t the point of learning martial arts. Internal martial arts, in particular, are an ego-dissolving activity, not an ego-boosting one.
If your teacher says something that you think you already know, do you feel an urge to inform them of that fact? If your teacher says “Do XYZ”, is there a part of your mind that wants to respond with “I am doing (trying to do) XYZ”? If so, that is the part of your mind that is holding back your progress. Usually if a teacher gives an instruction there is a reason, so start with this as your basic assumption, and instead ask yourself “Am I really doing XYZ? How could I do XYZ even more?” Ask questions if you don’t understand, but resist the urge to object, rationalize, or explain, as no good can possibly come of it. Not only does it shut down the learning process, it puts you in the wrong frame of mind for training, which is a kinesthetic activity, not a verbal one. As my sifu would say, “Talking does nothing to improve your kung fu.”
This is the meaning of “beginner’s mind”, or, as we say in Chai Tea Tai Chi, “come with an empty cup”.