From Anonymous, Rinkworks
Customer: "I lost some of my files. I archived them, but when I went to retrieve them, they were gone!"
Tech Support: "What program did you use to archive your files?"
Customer: "I used DOS -- but now I can't find them!"
Tech Support: "Ok, what program are you using to do this?"
Customer: "I used 'undelete', but they aren't there."
Tech Support: "Uh...what command did you use to archive your files?"
Customer: "I used 'del' and the filename."
It turned out that the guy had been deleting files, which would free up disk space (he liked that), and when he wanted a file again, he would undelete it.
Apparently he actually got away with this for a while, until he discovered 'defrag', which overwrote his deleted files.