I've got a co-worker that's been trained in the use of handguns and had the clearing procedure embedded in his head fire a round in his apartment. At the academy everytime we received our guns or put them away we had to say and perform the clearing procedure. Safe place safe direction, weapon level with the deck, finger off the trigger. Hit the Magazine release three times. Slingshot the slide three times. Visual inspection (look in the chamber). Physical inspection, top bottom top (stick a finger in the chamber then the bottom of the mag well then again in the chamber). WEAPON IS CLEAR SIR! Well anyways after one of his quals after the academy our firearms instructor told him he needed to work on his draw and trigger pull. He told him to clear his weapon and practice dry fire drills aiming at a post it note at home from time to time. Well a few days later he decided to do some drills and his first draw he fired a round right through the center of the post-it note and through his neighbors apartment. Luckily no one was home. What happenned was he half assed the clearing procedure and racked the slide then dropped the mag. He got in A LOT of trouble.