Not an egregious "error" - more overdue maintenance - but:
Garage rollover door cable snapped, about 10pm, while bike-fettling. I had no idea what had happened; bang, then door slunk down one-sided.
With the door fully open (and in the dark), you can't see the mechanism, and thus work out what the heck's gone wrong. I jiggled about with - in fear of head injury - then retreated to google+youtube.
Thus figured out what had broken, but no idea how to safely secure the garage without injury. Moved more valuable stuff indoors/elsewhere. Then hacksawed partially thru remaining cable before losing my nerve. Then I did some more jiggling and the remaining strands snapped - luckily it was now slightly jammed in the door frame, so didn't crash down. I managed to lump it back into the runners, and eased it down+shut. Locked OK.
I spent that hour expecting one of two other, bad outcomes:
- admitting defeat, and leaving garage insecure overnight. Or (more likely):
- door falling on me noggin, doing Grave Damage [no i did not fetch my only-worn-under-duress h*lmet, dear reader!!!
Went to bed VERY relieved (after quick shot of brown fluid made in Ireland).