Massad Ayoob likes for his people to have the index finger bent and up on frame. That’s good, though for some of us with weaker vision it’s a problem. We see bent fingers and assume that the bent finger is on the trigger. For a number of other reasons, the bent index finger is smart money. The rigidly extended finger can snap back into the trigger guard with enough force to depress the trigger and light a primer. The bent finger drops into the guard vertically, lessening the chance of a premature blast
Similarly, if someone jumps out and grabs at your nonholstered firearm, your straight finger can be trapped or the gun can be forced into the rigid index finger, hyperextending it
The arched index finger flexes and is stronger for being bent. The chances of injury lesson.
If we follow the middle rules and enforce them by visually confirming these physical safety checks, we vastly lessen the chances of a tragedy. Our almost religious adherence to them reinforces our belief that the firearm is loaded and makes us look hard to identify that threat before firing. They support Rule #1 and #4.
The physical safety checks are not “range-safety rules.” They are life safety rules. They govern all conduct of armed persons everywhere and at all times.