The difference is that those composed operators (versus laypersons) have extended their comfort zones through intense mental focus and training. They've actually "been there" through their training thousands of times in their preparation for the battle.
Life is a Live-Fire 360 Degree Environment
My partners and I constantly admonish our officer-students to scan before they reluctantly reholster. Events, the suspect(s), whatever - want to suck your attention and focus into a tunnel. Without understanding that this is a negative phenomenon that we must work hard to break, we'll miss accomplices or other threats or relax too soon and get ambushed by some unseen attacker. This tunneling of vision and attention can be even worse in low or subdued lighting. A flashlight and its beam of light can work against full circle attention because of the limited field of view.
Fortunately excellent training from people such as the trainers at Strategos International and others are making excellent low light training available. But telling officers about it is not enough. They must experience chaotic 360 degree threat conditions in training to fully appreciate and prepare for the threat. In the training realm, low cost innovative drills utilizing airsoft munitions are a great way for officers to be forced out of the tunnel and to learn to expand their attentiveness and awareness. I believe it was members of the L.A.P.D. SWAT Team that once said, "Training should be larger than life but survivable."
Out of the Tunnel and Into the Light
Limited thought and action is the result of SNS and lack of training to overcome its effects. The metaphorical walls of the tunnel can be real on the street and can hurt you. Expanding that cone of vision to more successfully work for you takes mental and physical preparation. Don't miss what's indeed out there and can hurt you. Train to work both mentally and physically within a 360 degree world - in can be done; now do it.