Lynn Young Sensei had a question; Here is the THIRD part of my answer.

Two things happen when you (any human) is startled: Your modern brain (neo-cortex) goes into shutdown and your primitive brain (amygdala) takes over; and as a result of glandular secretions coming from the amygdala your muscles go into major reflex response. In simpler terms "fight or flight" takes over and your fine motor skills go to pot.

When this occurs, you body will subconsciously react in the way you have trained your muscle memory. If you have trained yourself to run away, then you will try to run and if you have trained yourself to attack then you will attack. If you have not trained any muscle memory at all then you will stand in slack-jawed immobility as you are ploughed under by your attacker. You will do instinctively what you have taught yourself to do.

In this respect the stock answer ("you fight the way you train, so train the way you fight") is 100% correct. The problem lies with knowing exactly what you are training to do and why.

The second thing that happens: When startled, YOUR FINE MOTOR SKILLS GO TO POT. It is all well and good to practice fancy grabs and holds and joint locks and disarms in the dojo but in real life - uh, no. You can try for your fancy wrist grab but I doubt it will work. Instead, you should train for macro movements; this means large circle jujutsu instead of small circle. Take a look at krav maga; most all of their techniques are macro movements. If you are in a startle-response situation that is just about all you can pull off.

In a lot of cases modern self defense training is built upon false or obsolete assumptions. Back in the 1920's it was all well and good for Sergeant O'Malley or Corporal Clancy to stand around smacking his nightstick, causing Johnny Rotten to slink away down the alley in fear. Not going to happen these days, my friend.

Lots of folks have figured out the cops are typically too far away for anything except paperwork and body bags; funny how they never seem to credit criminals with the same knowledge. Most criminals and thugs HAVE figured out the cops are not around, and they also know that if they cut you or shoot you then everyone is going to concentrate on saving you rather than catching them. The new paradigm is "kill first, rob second". Another rule of thumb for criminals is "rolling drunks is easier than mugging, mugging is easier than a stick-up, sticking someone up is easier than bank robbery". That one HAS been in place since the days of O'Malley the beat cop.

DO NOT expect a criminal to walk up, pull out a weapon, wave it around and say "dis is a stick-up, yah see. give me allayuus dough, yah mug". Probably the first time you see a weapon is when you are cut or shot by it. So train for that scenario instead of the one where you calmly grab the gun, twist it out of the bad guy's hand and then hold him with his own gun until the cops arrive.

Final thoughts for this response:
1. Training to prevent being startled by an opponent is the best way to develop zanshin (the remaining spirit). This is "situational awareness" in modern terms. If you are not startled, then you CAN use all of your higher-level training to your advantage.

2. Training to handle sudden changes in your situation is the best way to develop jikishin (the direct spirit). Saseong McNeely calls this "stress innoculation training" and it is.

http://www.mytkdworld.com/M-CAT/BecomeM-CATCertified.aspx

3. Training to develop confidence and conditioned responses is the best way to develop mushin (the null spirit). This is all up to you, and if you are wondering "how" then you did not read the first installment of this discussion.