I get tired of hearing that phrase or seeing it printed in the paper. Guns no more "just go off" than a stapler "just happens" to spit out a staple. Guns no more "just go off" than a camera "just happens" to take a pictures. Guns no more "just go off" than Britney Spear's hair "shaves itself".
All of these items require some sort of mechanical pressure and action to do their thing. Yes, there are instances of mechanical failures, and those are truly accidents, but 99 times out of 99, guns go off because some idiot put his booger hook on the bang switch and pulled.
'Just sayin', ya' know.