Probably about the dumbest thing I have done as a user/manager happened years ago. I had several boxes of diskettes that needed to be erased. I was just about finished with the project, getting tired of messing with it and entered del *.* -- Oops! no A:\ - BIG mistake. Gone!!!! My entire Windows directory wiped clean. No backup!!
Live and learn!
I can admit it now, but about ten years ago when working at a hospital we were about to do some changes to the payroll database. The quickest way at the time was to FTP the database over the network. I was talking to a co-worker and instead of entering the FTP put command I typed in the FTP get command. This basically wiped out my database with a zero byte file.
Luckily it was a light day and after 4 hours of restore time from a DDS-2 tape we were back in business. I stressed the entire 4 hours and praying that it was a good tape.
Centuries ago, when I was a gross tyro at PC security, I thought just blithely installing an anti-virus program would protect me. I didn't make time to learn about updates or doing regular scans. I thought it would be self-sufficiently omnipotent for eternally. I'm not sure if it even could be set to scan inserted floppies, so that never happened.
An equally goofy and careless customer sent me an infected floppy with the Chernobyl virus on it. That beast not only dismantled all the data on my hard disk, it somehow fried my chipset. Our local technologist couldn't even fire up ol' Bessie.
I was able to get the insurance company to agree it was an act of vandalism and did get a new PC out of it. Still, it was chastening and a reminder that nothing is really self-maintaining.