In the preface of Wang DiXian's tai chi Nei Gung 24 styles, he wrote (my translation):
All (tai-chi) lineages have their own systems of tai chi nei gung, it is unfortunate that most didn't know about it or only practice a few styles, the reason is to "teach or not to teach".
Wang was certainly talking about a phenomenon that he observed, and he had the kind heart to publish the Wu/Chang 24 styles in good will, despite the fact that he probably did it against his master's wish. The interesting thing is that I know some guys who have been doing tai-chi for a number of years, after they have a glimpse of Wang's book, shook their head and commented "what's great about it?"
And they are right, what is great about some physical movements if one don't know how to stimulate one's internal power (nei gung) through the movements. A teacher is needed with some good instructions. The question boils down NOT to "teach or not to teach", but to "know how to teach or don't know how to teach".
Finding a good teacher is important, but, as an amateur teacher of the practice for a number of years, I have this personal revelation: "finding an intelligent student who is willing to learn is even more difficult". Which, in the final analysis, boils down to my assertion: "It is very difficult to learn tai-chi nei gung" despite the fact that one knows the bodily movement (like having access to Wang's book, or for that matter, information on other systems of tai-chi nei gung as Wang said), and secondly one gets hold of a teacher who know how to teach the internal movements and feelings.
I shall further explain the WHY towards my assertion in some future posts, stay tuned.