For the first show I worked on at Drama School, I was working as part of the LX team. We were rigging a bar onstage, and someone asked to borrow my knife to cut some tape. Handed it to them, they gave it back. Finished rigging the bar, bar flew out. All fine.
At the end of the session, I realised my knife was missing. We all searched high and low, but to no avail. I put up signs, sent out an email - nothing.
(I bet you know where this is going.)
Four weeks later, the last show came down and we all piled in to do the strike. I was in the second theatre rigging for another show, when the Prod LX came in, holding my knife. Turns out, I had put it down on top of a lantern while my hands were busy, and forgotten to pick it up.
There were 80 cast onstage for the majority of the opera, so if it had fallen off the lantern, it could have been a lot worse. LESSON LEARNT.