Well said, DeeD! I would only add that training against UN-trained opponents might be just as important. With fellow martial artists we sort of know what to expect in a general way; with an untrained, crazy, anything-goes type of opponent you find out if your art REALLY works. I found this out only after years of sparring with other trained fighters. Spar with a Taiji guy - I knew what to expect. With a Taekwondo guy - yep, I knew what was coming. Judo - same thing. But my first match-up as a bouncer with a crazy guy really showed me the holes in my techniques and in my tactics. This guy did stuff that no sane person would do, and for him it worked because he caught me off-guard; I was still in the "dojo-mind".