The source code for a commercial product we sold was safely backed up to 3 floppies, with a master in the fire safe, and several "working copies" throughout the department. This was in the days before desktops had hard drives, and floppies were the only storage we used.
One programmer needed to work on the code, so loaded one of the working copies. The load failed with a disk error - which was not unusual. So he got another working floppy. Same result. Eventually he had determined that none of the half-dozen or so working copies loaded, so he fetched a backup floppy. That failed. So did the next, and so did the last remaining backup. That's when he asked me for the key to the safe to try the master. I did not believe that ALL the disks were faulty, and so tried them in my machine - and sure enough, none worked. But before fetching the master floppy, I took a look at his computer - and discovered that his floppy drive was faulty with the head being permanently supplied with write current ... so every floppy he had tried to load had been erased.