....forget to make sure the tag end of your film engaged by seeing whether or not the rewind lever spins.
Ah - the film days
I was a Snap On Tools dealer in a former life. Several of us took a trip to the Mount Carmel Il plant for a tour. I took some awesome pictures of all kinds of machining operations, chrome plating, hand fitting of pliers joints, etc. These were going to be awesome.
Even though I knew to check that the film was engaged, I didn't this time. It wasn't.