About 45 years ago, a friend of mine was sitting in the front seat of a ranch pickup with a loaded 30-30 lever action with a shell in the chamber and the rifle on half cock safety. He was sitting there idling away the time, absentmindedly pulling on the trigger. After doing this for about 15 minutes, the safety slipped, the gun went off, a hole appeared in the roof of the pickup, and he got a case of powder burns and ringing ears.
It was an old gun, but the object lesson that the half cock safety might possibly slip has not been lost on me.