Lucky, indeed!
The absolute dumbest thing I've ever done, PC-wise, was when I upgraded from DOS 3 to DOS 5 (almost everybody skipped DOS 4, a true disaster). At the time, I had a PC with a 330 MB hard drive, set up as a veritable alphabet of 32 MB "drives" (from C: to M: if I remember correctly). DOS 5 was the first to support "drives" larger than 32 MB. I also had a tape drive on the PC for backup. I had a batch file that I used for backing up "drives" to tape. I wrote a master batch file that called my backup batch file one time each for each "drive". I started up the batch file, watched for a bit as the backup software was writing to my tape.
Backing up 330 MB to tape took a LONG time, so I took a long lunch and had a couple of beers. When I got back, the backup had completed, so I reformatted the HD, installed DOS 5, installed the tape drive software and restored my files.
Well, that was the plan. The only problem was that I'd screwed up the command line and set it to overwrite instead of append, so the only thing on the tape was the contents of Drive M:. Which, at the time, happened to be empty. So was my backup tape.
Three years of work (millions of dollars of customer quotes and proposals) gone. I had to have my sales guys fax me the quotes I'd written so I could recreate them.
I simply cannot describe the feelings I had when I realized that my backup tape was blank. Well, not in a family-friendly place such as this forum.
I am happy for you, Ludwig!