I took a one day seminar on "tactical scenario survival" (or something to that effect). It was excellent with lots of good and surprising info, including videos of actual situations. 

One thing we learned is that most people lose it when surprised by a violent threat. Many run in a random direction (over others if necessary). Some just stand there immobilized. Often police who are sharpshooters at the range now miss the threat up close. 

Meanwhile the armed perpetrator has his blood up already and is more prepared. 

Guns help the perp way more than the victims.