I was working on my final project in a class in undergrad on the campus VAX. VMS had a versioned filesystem, which is to say that every time you saved a file (like your source code in LSE), it would create a new file (e.g., FINAL.COB;23). I was getting confused by all of the versions of my project so I decided to clean some of the older ones out:
DELETE FINAL.COB;1*
DELETE FINAL.COB;2*
I had to run to the data center the VAX was in halfway across campus to beg the sysadmins to restore $STUDENTS:[DRWHO.CS1337]FINAL.COB;* from the hourly tape backup (at least there was that) and re-debug the last two functions so I could hand it in before midnight. Lesson learned: Don’t worry about cleaning up your workspace until after you’re done.