Doing a search for something recently, I tripped over a post by Ben Cole that addressed the importance of a living, breathing instructor. To paraphrase it, he described how one of his instructors corrected him as he worked a particular move, telling Ben to put his foot HERE, not THERE. The correction was repeated, and somewhere along the way, Ben asked "why?" The instructor told him, essentially, "because that's where your foot has to be to do this." In time, Ben came to realize the why -- which amounted to because that's the right place for the foot. That's not a correction you're going to get from a video tape. And it's not a lesson you'll learn without the teacher being there to notice and correct it. (Whether the student will listen or the teacher will bother is a different discussion.)