Training For The Unexpected.. YOU CAN'T
Training for the unknown-unexpected is impossible, because its unexpected and unknown! What does happen is, you default to your training... what ever it may be, and/or your survival instincts. We train for the expected, the alert situations and high percentage confrontational situations we're exposed to.
You'll see in this video of the detroit headquarters shooting two things, one is the defense reaction, which is moving-cover, and the second is laying down repeated rounds (Bad Guy).
Having a fast draw/reaching for your weapon is great, if your in a obvious confrontation, but when something happens unexpected you need to MOVE and COVER. From an offensive stand if your laying down fire while retreating to cover or if no immediate cover is available, repeated fire at your target can save your life by allowing your target NOT to have a clear and unchallenged shot.
Police officers who are trained in this tactic when they might be exposed in a traffic stop or exposed while taking on fire in a situation, the response of repeated fire at their target may save their life, hi-capacity magazine/weapons (G19) for example can lay down repeated rounds before needing to reload.
The natural instinct for anyone looking at a exploding gun shooting/pointed at them... is to DUCK/RETREAT/COVER.
check out the video in this trauma situation, very lucky no officers were killed, GOD was with them. You can't be ready everywhere 24/7/364.