super-oops with computers
The worst computer mistake I ever made was on my C64, way back when I had only one floppy drive. I wanted to make a backup copy of a disk, & the disk copying program I was using had to format the backup first. It was halfway done with the format phase when I realized I was holding the blank floppy in my hand and that the disk I wanted to copy was being formatted.
super-oops with computers
The lesson I took away from that mistake was to write-protect the source disk before thinking of starting a copy.
That force of habit is still with me today. If I format, image, or copy anything & have more than one SD card involved (including micro-SDs in SD dongles), I flip the tab to "Lock" on the source card.
super-oops with computers
@arielmt Good habit!
But what about USB flash drives? 
super-oops with computers
@Tobi *an ominous 'is the villain really banished' musical sting*