In a study done by the FBI in 2014, it was found that most active shootings end in 2 minutes or less. That’s not enough time for law enforcement to arrive. So when you start hearing gunshots in places you shouldn’t be hearing gunshots, you don’t have much time to think about what you should do.
When any emergency strikes, be it an active shooter or a fire, the natural response for most people, surprisingly, is not to do anything. Our brain is predisposed to assume that things will carry on in a predictable way. When the pattern is broken, it takes a long time for the brain to process this aberration.