I propose a re-write of that rule. Instead of “Treat every firearm as if it is loaded,” how about...
“IT’S FUCKING LOADED.”
Cup of coffee in hand, starting your day at work, IT’S FUCKING LOADED.
25 years of experience, cleaning the damned thing in your garage? IT’S FUCKING LOADED.
Brand new gun straight out of the box? IT’S FUCKING LOADED.
I don’t even like calling it a rule. It’s a fact. Not a rule, not a guideline, not a suggestion. A fact.
Sure, it’s hard for some people to wrap their heads around, but I think of it this way, even when I know, and I’ve triple-checked the chamber to be sure it’s empty, it’s STILL FUCKING LOADED.
Just the other day I was practicing draws, and after I put the empty gun down on the counter, with no ammo in the same room, and picked it back up, I paused and stupidly thought, "I don't really have to check if it's loaded." I then thought of all the trouble that would occur if I was somehow magically wrong. The expense of repair, the damaged hearing, the shame, the likelihood of being kicked out of our complex, and the possibility that I could actually kill someone on accident. Then I thought of how it all could be prevented if I had just taken ONE SECOND to check the chamber again.
Then I checked the chamber.
Think of it as developing muscle memory if you have to, but check that fucking chamber, because IT'S FUCKING LOADED.