I once had a wonderful converstaion with Kuroiwa sensei when I visited Tokyo about ten years ago. One of the things he said was that if you are a good teacher, something it took you twenty years to learn will take your students ten. Then they have ten years to be better than you are.
There used to be the old Japanese idea that you had to essentially steal a technique. Your teacher would do little if any explanation. You had to figure it out for yourself. That has some validity but at the same time it essentially means that each generation of students must re-invent the wheel for themselves.
I have friends that train with teachers that seem to prefer not to give away too much. In fact they have a hard time getting the teacher to show them much of anything. I had one fellow who trains with a senior Japanese Shihan come to a seminar on teaching Aikido to the police because he wanted to do applied technique. He said that he had asked repeatedly for his teacher to show him and was refused. He said that only on a couple occasions over the years at demos had he seen his teacher do anything in this vein. Now I can understand that a teacher might not wish to teach that type of stuff to the public (O-sensei certainly didn't, hence a certain amount of misunderstanding about what his Aikido was)but this fellow is the senior student of this teacher. He is highly ranked and has been training and teaching for going on twenty five to thirty years. He told me that he is quite frustrated because his teacher is getting old and if he doesn't pass on what he knows in this area it will go with him when he passes away.
I have been fortunate in my training to have had teachers that have done everything they could to pass on their knowledge. Saotome Sensei has thrown out the whole spectrum for us to see. He has held back very little and has worked very hard to get us to understand what he is teaching. My other teachers, Hiroshi Ikeda sensei, Mary Heiny Sensei, Tom Read Sensei, William Gleason Sensei are all masters of the explanation, literally giving away what they had to work really hard to get themselves. Some would say that the students are getting their training too cheaply but I think that doesn't matter at all. No amount of explanation will make any difference to the student who doesn't put his all in to the training. But with teachers who are willing to share their knowledge in this open way and really teach, we may be able to have what Kuroiwa Sensei hoped for and that is a generation of students that can be better than their teachers because they don't have to spend the time rediscovering what the previous generation had to.