I had been working on a major change to some code on a COBOL system. For safety, I copied the original files to from *.COB to *.COBOL. I then spent 3 days working out the changes needed, and testing them.
I got it all working and error free, so I went to delete the original files, but I only got as far as "del *.COB" befiore hitting return. WAH! I copied the .COBOL back to .COB and started over again. As I knew what I wanted to do this time, it only took about a day to re-do what I had deleted.
Another time, I had been working late on a presentation for my boss and I went to rename it, right click, select Rename from the menu, hand slip, click, file gone! Delete is right above Rename in the bloody menu! Luckily, I had sent a copy to someone to start checking over about 20 minutes earlier, so I had a recent backup to work with! But that is what happens, when the boss comes in at 5:30 in the evening and says he has a presentation at 10am at CeBIT the next day and needs 40 slides...