Very nice little video! Even though I have been using LF cameras for about 50 years now (!), I still occasionally make his first and last mistakes, always if I have gone too long without using the camera, and as he puts it, "lost the muscle memory."

For the first, forgetting to shut the preview lever on the lens, I try to remember to always fire the shutter once before I pull the dark slide. If the shutter won't fire, I've caught the problem before exposing the film at full aperture.

For the last, forgetting to flip the dark slide, I've never found a failsafe. Sadly I have on (rare, thank goodness) occasion taken out the holder after making an exposure, and noticed that I either have two "black side out" slides when I know I have only made one exposure, or two "white out" slides when I know one side has been exposed. In either case, after muttering choice words, I put the holder in with the completely used holders, knowing that when I develop film I will have one exposed and one unexposed negative. I have wasted film, but will at least have one image as I intended.