I feel like I'm pretty good at archiving and back up stuff, but I do find I've lost something every year. Today, it's the remixes I made with a random remixer app that I made dependent on the Spotify API, which no longer works. I uploaded those to Mixcloud, kept no other copies, and just learned Mixcloud deleted them for copyright violations. (I thought Mixcloud was all about mixes and remixes, though?)
Besides the lesson about only having one copy of something on someone else's storage, I gotta remember that if I generated something with a program, I can't just assume that I'll be able to run that program again years later to generate it again.