Well, this could easily be an endless list. But here goes with a few...
There are no light meters that fit my requirements for high sensitivity (wide EV range, especially on the low end), solid, durable, and reliable construction, and a size small enough to carry in your pants pocket.
36 exposure rolls of film. They should be 35 exposures so that they all fit (sort of) on an 8x10 sheet for proofing an entire roll at once, and fit in a normal notebook sized archival sleeve page.
35mm cameras that don't have a frame on the body to insert the end of the film box to help you remember what film is loaded.
Subjects that move faster than I can meter anf focus.
Grand vistas that require me to walk more than 30 yards from the car with a heavy Ries tripod and a Deardorff 8x10.
Forgetting whether or not you already put the sodium sulfite in your fixer.
Not having a spare camera battery when you need one.
Not having a store that sells film, any kind of film, nearby when you run out.
Having your 8x20 banquet camera fall off your tripod while carrying it across a busy street. That is not only disheartening, but embarrassing too.
Dropping your light meter in the stream you're standing in.
Forgetting to put your cigar down before bringing the camera up to your eye. This usually happens when drinking beer.
