I'm not sure anyone is so absent minded as to forget where they've stashed firearms. When I was living alone I probably had 3 or 4 handguns hidden in certain areas, but it's not like I ever forgot or came across one and was surprised to find it.
On the flip side, it was almost comical when my great uncle passed away and my grandpa and mom were cleaning the house. I think they found 7 or so handguns stashed behind books, on top of cabinets, and in drawers. THEY were certainly surprised every time one of them found another firearm!!!