I think by "overlap" y'al are referring to the redundancy of safety rules, right? How one safety rules is kind of a fail safe in case you break another? One of my trainers said - if you could be 100% certain you would never break rule #3, you could disregard rules 1&2 and still never have an tragic accident. It made sense but who's 100%? So, like the overlap
The overlap in the safety rules is important, and it is true that most injuries occur from violating every safety rule at the same time, but this is not always the case. In rare cases, mechanical failure can cause a firearm to discharge when the trigger is not touched. In these cases, rule 3, which states to keep your finger off the trigger, is not sufficient. Cases of mechanical failure where the trigger was not touched are the only times when I would use the term "accidental discharge" rather than "negligent discharge." And while these cases are exceedingly rare, they can happen during any type of manipulation of the firearm, such as when the safety is disengaged, the bolt is closed, or the decocker is activated.
For this reason, the most critical safety rule is to always keep the muzzle in a safe direction. If this rule was never violated, there could never be an injury. As a Range Safety Officer, I emphasize to people the importance of controlling the muzzle, and I especially mention the importance of controlling the muzzle when the gun is UNLOADED. As several honest people have admitted on this thread, even very careful people can momentarily forget that a gun is loaded. It is critical to habitually control the muzzle at all times, whether loaded or unloaded. Ingraining proper habits makes a huge difference in case there is a momentary lapse of the conscious mind. I always keep in mind that most accidents happen with "unloaded" guns.
Despite the critical importance of keeping the muzzle in a safe direction, no safety rule is actually "the most" important. All of the safety rules overlap and work together to create multiple layers of safety. And because humans are not perfect, layered safety is critically important. As I mentioned earlier, in most cases of injury, every safety rule was violated simultaneously. By maintaining a good focus on following all the safety rules, a momentary mental lapse in one area should not even come close to causing an injury. It should, however, be a learning experience and a time to review procedures. Perfection is a tough standard, but it should always be the goal.