Reminds me of a story from my youth. HS German Club planned a trip to Europe - pretty much on the cheap. Got some language teachers to chaperone the group. Great time had by all in like 7 countries.
This was 1964 and the "Instamatic" camera was a recent invention. None of us on the trip were particularly camera savvy so most carried these point-and-shoot-with-the-drop-in-film-cassette cameras. I happened to carry a really cheap 35mm SLR I'd bought from Sears and Sawbuck for maybe $13. One of the girls in the group pointed out that once the Instamatic film cartridge was used up, one could break the cartridge in half, dispose of the empty film side and keep the exposed side. This would save precious space as we accumulated treasures from various countries. Sounded good to several who followed her advice. Unfortunately, she apparently was unaware of which was the film supply and which was the exposed film spool. Low and behold upon presenting said broken cartridges for processing back in the good old U S of A, several folks found that they had pitched the wrong half.
As I had used the more ancient technology, my pictures were in great demand - and of course the girl who didn't know which side was which was somewhat of a pariah at our little club get-together a couple of weeks later. Guess you live and learn - sometimes the hard way.