It's not about Rule One. It's about the other three rules
, which idiots throw out the window as soon as they've checked, double checked, and done whatever dance to the moon gods they think is necessary to get the gun unloaded and keep it that way.
If you throw out 75% of your multiple, redundant layers of safety, eventually you'll shoot someone or something you shouldn't have shot.
And then you'll go online and claim it was just "one moment's inattention" and "just ONE little mistake" that bit you... when in fact it was a lifetime of overconfident but stupid gunhandling that did you in.