I don't post this with any joy in my heart. In fact, I would never tell anybody about what a fool I am if I didn't think somebody could learn something from it.
The beauty of the four rules is the built-in redundancy. In general if you have a mental lapse on one of them, the other 3 can still save your bacon as long as you follow them. I have never had a round pop out of a weapon somebody handed me, but I _nearly_ handed one to somebody with a round in it. I "emptied" Mrs. Halfront's glock and was about to hand it to her when she asked me if it was clear. I assured her that it was and racked the slide. Sure enough a round went rolling across the floor and we both just kind of sat there in silence for a moment.
I learned a lot in those two seconds.
I'm forever grateful that I was following the rules. I was treating it as loaded even though it "wasn't", I kept it pointed in a safe direction the entire time and I kept my finger off the loud button. The rules, the rules the rules. The rules exist specifically because a person could do something foolish, and I did. The rules didn't keep me from doing something foolish, they just kept me from paying an unbearable penalty when it happened.