Many years ago a buddy of mine had a S&W Model 19 with a 4" barrel. At the time he was living at his parents house, and kept the gun around for home protection. He would unload the gun, and dry fire it at the TV at night for practice. One night he told me he was practicing, then when he decided he had enough, he loaded it up, put it back in its holster, then set it on the end table. He was going to put it away during the next commercial. Several commercials came and went, and he completely forgot about the gun. He happened to look over at his gun at one point, then decided to practice some more, so he pulled it out, and shot a hole right through the center of his TV. He said that he was glad he didn't line up the sights on his sister's cat for that shot. I ended up buying that S&W from him.
Well, this triggered a memory. One day while practicing drawing and firing, I quit and loaded my pistol. I was in my shop, and later decided to do it again. I drew and fired for real. Good news is that my imaginary target had always been a stack of wood, or other inanimate object. The good news is that all that dry fire had been helping. The bullet hit the 4x4 I was going for about an inch from the knothole I was using as POA.
It was such a 'non-event', I had completely forgotten about it.
It does show that a person can forget if their firearm is or isn't loaded. Now, I just keep them loaded and won't dryfire unless I double check, and I triple check several times afterward.