I was doing phyical maintenance on a old laptop of mine where I fried a cable because I plugged the battery in and forgot to plug that cable in but I forgot to unplug the battery before plugging that cable in and ended up frying a cable when plugging it back in
I once tried partitioning the disk i was running on because i was new and didnt know that wouldn't work, cfdisk now has a warning if you try to do that
I had to extend the boot drive on a VM that also happened to run the application our entire company used to make products. This was back in the day when extending VM drives took forever because of the way the hypervisor worked. I only had a small window to do this between our Europe plants going offline and the US plants starting up.
So I used a community tool that would extend the drive in seconds. Turn the VM back on and queue "NTLDR is missing". I also discovered that the backups for that server hadn't completed successfully in so long there was nothing to restore from. In my effort to save 30-45 minutes, cost me 8 hours completely rebuilding the server and a day of lost production in the US plants.