Here's another. Some time ago I was shooting with my Pentax LX, and really enjoying the silky smooth film advance feel. Ball bearings, I suppose. Then I noted that I'd run through 35 exposures on what I was sure was a 24 exposure cassette, since I almost never bought 36 load. Yep. Hadn't loaded the camera, a camera I'd been using for 8 or 10 years. Doh!