A sentence in a pilot's flight manual reads, "When you enter the cockpit of this aircraft, you become part of a system over which you have control…both in terms of operation and safe handling. You are the only one that can make the system safe or unsafe."

This is true of a shooter as well. From the time you pick up a firearm, you became part of a system over which you have complete control. You are the only part of that system that can make that firearm safe or unsafe.