Gun shops are the worst, for cavalier attitude. There are too many people there and too many of them are inspecting a firearm for possible purchase. And they are talking to a salesman on the other side of the counter. There really is no place to point that muzzle safely. Now the chances of a display gun being loaded are remote, but so what? That doesn't excuse breaking rule #2 "Never point the barrel at anything you don't intend to destroy."
And then there are people bringing guns IN to the shop, for repair or evaluation or just to consult to find out where some fun rifle may have come from. And a rifle goes on the counter pointing directly to one side. And no one opens the action half the time. A strange gun belonging to just some guy, and people are just handling it like it was nothing. And pointing it at me. A violation of Rule #2 and Rule #1 "All guns are ALWAYS loaded." The gunstore sales people always open an action before handing you a weapon to inspect. But people can forget.
Same with your finger resting on the trigger. It's the easiest rule to forget. The finger just WANTS to go there. Though I have seen a rash of people instinctively following good finger on trigger discipline. That's good.
For me personally a situation exists that I have to always stay on top of. When I convert my .45 to .22 I have to field strip it. It's important to TRIPLE check that the magazine is out and the chamber empty, because when field stripping you are gonna have that barrel pointing at SOMETHING you'd rather not shoot, and mostly me. "But I dropped the mag and worked the slide 4 times to be sure there was no round in the chamber and it still went off!" Someone might say. Well what if the extractor was broken and couldn't yank that last live round out of the chamber? I never want to be that "someone". I jam my pinky down the empty cylinder after looking at it. I see it is empty and I feel it is empty.
Chuckles thinks I am over-cautious. Better over cautious than over-dead, I figure. Keep the blood on the inside of me and the air on the outside of me. Chuckles poo-poos the Four Rules. "Sometime the gun IS unloaded, duh! How can you NOT point the gun at something you don't want to shoot unless you buy and mount it permanently at a stand at the range and never move it?" Chuckles is a FIRM believer in the "no finger on the trigger." And as long as he adheres to that he is safe enough. You have to violate more than one rule to hurt someone, after all. If you have your finger on the trigger and negligently discharge, but you were obeying the other 3 rules, then the barrel won't be pointing at anyone in the room or in line with the barrel through to other rooms.
It seems all negligent discharge cases start with "I became complacent." That's why I am typing this now. To keep myself from being complacent.
Here are some people that regret their complacency. The infamous "This is a Glock .40 and I am the ONLY ONE trained enough to ~KABLAM!~ Ow! My leg! I just had a negligent discharge!" Guy.