Back when disk compressors (Stacker, DoubleSpace, and such) were a thing I was cleaning my 85MB hard drive to make space for some games, found some massive file I wasn't using, and promptly deleted it, which did indeed free a lot of space.
Way too much, in fact.
Turns out DriveSpace or whatever Stacker clone Microsoft had built into DOS somehow exposed the file in which it stored the compressed file system within the compressed system itself, allowing the user to delete it if they were stupid enough. So, when I deleted it, hilarity ensued.
In the end I think I was somehow able to recover the drive by booting from a floppy and using undelete or something like that, but it was a learning experience to say the least.
first time trying Linux, installed Ubuntu. Over a few months I made a few mistakes but nothing major... untill I tried to delete VLC. Saw on some random forum that something called MKV was better. Googled how to delete a package and it turns out I deleted every dependency for VLC and not VLC itself. Totally nuked everything.
Did something similar when I was still learning Linux. Had some issue with Python. Decided to reinstall it. Did a force remove and my computer restarted immediately. I was brought back into a shell but basically nothing worked right. Turns out Python is a dependency for a lot of things in Ubuntu. Who knew? :D