Actually that’s rule #2. Rule #1 is that all guns are always loaded with a round in the chamber.
I recall a story a freeper told where he was at his friend’s house trying out the new trigger in his friend’s handgun. They unloaded the weapon with the rounds sitting on the table. He squeezed off a few dry-fires at the water-cooler in the corner of the basement.
Then the friend’s wife called them up for dinner. The freeper went into the downstairs bathroom and when he came out, there was the gun and the rounds still out sitting on the table.
He picked up the gun to dry-fire at the cooler a couple more times before heading upstairs.
“BANG!”
At least it was just a water-cooler! For some odd reason his buddy had reloaded it with new rounds from the box, rather than just replacing the rounds he had taken out.