In martial arts, nobody wants to get hurt. If you fight or seriously train, it is going to happen sometimes. Everybody wants to dish out punishment but nobody wants to receive any. Ask any good fighter and they will tell you they've had their share.
It's cool to win and I prefer to do so by stoppage as opposed to decisions. Against opponents I have knocked guys out with punches, kicks, knees, etc., dropped guys with body shots (even breaking ribs), I've kicked opponents in the legs tearing up knees, choked them, arm (popping some ligaments). Sounds cool right to take out an opponent. But what about what one receives himself along the journey of Captain Badass.
As a combat athlete, I have had my share of injuries. The lists include ACLs, meniscus tears, dislocated fingers, broken a big toe, hyperextend joints (from getting hit along with submissions, hip out of place (trying to kick heads off with spin hook kicks), torn cartilage, 18 stitches around the eyes (head butts and punches), tendon shortening (years of throwing hard right hands), calcium deposits causing bumpy shins and forearm bones (from blocking bone on bone), slammed on my back (needing an adjustment afterwards), black eyes, split lips, swollen noses, sore jaws, crooked teeth, punctured ear drums, corneal abrasions, cauliflower ears, and a few more.
So in order to learn the way of inflicting pain on an opponent, one has to experience it. You appreciated the effectiveness of techniques applied to their fullest. No theory but reality for those who choose the path.