I'm really surprised how few comments there are in this section. My favorite story is a call back after rekeying a house. The old lady insisted that her old key still worked the door and she could open it. When I arrived I immediately identified the issue. The problem was explaining to her what she was doing wrong.
She put her old key in the door nob and "turned it". 'See the old key opens the door. ' I tried several times to nicely explain to her that she was not unlocking the door. All she was doing was using the key as leverage to open the nob. I showed her that I'd I locked the door the key would not work. I was there for at least 10 minutes before it finally clicked in her brain what was going on.