One of the comments on another post mentioned Aldo Nadi's duel. Nadi was a jerk, but he was the finest fencer in the world at the time (it's arguable, but most of Bruce Lee's concepts and strategy of JKD appeared to be directly cribbed from Nadi's book "On Fencing".) In that book he describes his one duel. It reads with the fuzzy clarity of someone who expected to die, remembering every detail. He knew that what he did, fencing, was not what he was about to do- dueling.
He was aware of the difference. Probably too aware, because the technical difference was minimal. He was almost frozen and he had to get over that- which he did- in order to access his skills.
I expected the fight to be hairier than anything I had ever experienced. Nadi expected the duel to be so vastly different from his training as to be alien.
George Mattson of Uechi-ryu tells a story in this article about a run-in after hours at a bar in an interesting part of town. At the time, he had a little less than twenty years of training in karate. I've met George and he is a superb martial artists, a superb teacher and I've watched how he handles the Uechi crew- subtly, respectfully, without throwing his rank around. He is clearly a strategist of high order. At the time he had been running the bar, including handling the frequent problem child. Lots of training and far from his first fight. George was way beyond where most people are when they start selling self-defense systems or street-fighter certificates.
To paraphrase the story, after hours a group started stealing the bar sign. George ran out- more balls than brains- and clobbered the biggest. The bad guy went down, blood everywhere. Then he got up and said, "You want to fight? Let's see what you got."
This is the looking glass moment. You've trained for besting a martial athlete. You've visualized taking on a knife-wielding psycho. Then what you get is someone who enjoys this. Win or lose, the worst beating you've ever received or handed out is several notches below what he does for fun. A trip to the ER for some stitches and a cast has all the emotional weight of a hangover- just the price of a little fun.
George got out of there- high order strategist, remember? But he still thinks about it. The smile still haunts him.
The looking glass moment. You get to something that you've prepared for as well and intelligently as you can and it's not what you thought it was. What do you do?
There are two things I want to say here:
Broadly, expectations can be the problem. Be prepared to let them go. You may not even believe you have preconceptions, but you do. If something ever happens and your first thought is, "That can't be right," ditch the thought. It happened, deal with it. Quickly. I've tried to say this a lot of ways- a survivor can come from any training background if he recognizes when he has entered unmapped territory and lets go of the map. And someone from any training can be killed by the training if they cling to the training in spite of the reality.
Narrowly, about George's experience. If you take your training as serious business and you train hard and play hard, imagine mixing it up with someone who takes your best shot and laughs because it is sooo much fun. It's been years since he met anybody good enough to hit like that! Yeeeha!
I've been in that mindset, and it's hard to stop. You see the look in their eyes when they slam you and they see your grin and they actually start to think that you're not human, not like the people they practice on.
There's another mindset too, where it is just a job: "Son, I get paid whether you go to the hospital or not. Make a choice." Martial artists have years of ego built into their training and to fight someone who has no ego about it is chilling and strangely comforting. At the peak, when I was averaging two a week, I spent a lot of time in this mindset. It had a cost, but it was even effective on the manic fight lovers.
There's too much information here to parse it all and I apologize for presenting it with such poor organization.
Boil it down: Here are a few mindsets you might not be aware of. Most people can't really comprehend them until they meet one. If you do, you may lose all confidence and your blood will feel like ice. If you can't get out, fight anyway. The skill is still there, you just need to get over the freeze and access it. But don't expect to get out unscathed. You can achieve these mindsets: the first if you push yourself and actually take punishment as a hobby (but you will pay for it later- numbness, arthritis, blurry vision, etc.). The second only (to my experience, so far) by exposure to the point that you burn your adrenal glands out, and that has a cost, too.
Most importantly, whatever you have experienced, you haven't experienced everything. When something new comes up, don't waste time trying to cram it into a pigeon hole. Let go and see it for what it is.