Most frustrating lost item incident....
I had to adjust the rocker arms on my '66 GTO...not a very time consuming project. When I had it all back together, I set a short 3/8 adapter on the trim pan that spanned the are between radiator and grille, reached past it, then came back to snap it onto the wrench and turn the last - very last - bolt, to finish the procedure.
It was gone. And I absolutely needed it for the last bolt - I could not reach it without that adapter, and it was the only adapter I had.
I thought, OK, maybe I hit it with my elbow. Checked the floor. Nope. Checked all around the trim pan. Nope. Checked the motor. Nope.
Re-checked everything. Nope. Bounced the car up and down multiple times in case the adapter had fallen down into the engine compartment. Got down on hands and knees, got flashlight to look under car in case it had rolled somewhere. Nope.
Circled the car, checking the floor inch by inch. Nope.
By this time, I was exercising substantial linguistic skills, and even inventing new ones. I was 30 seconds from being done, and stuck.
Finally I got down on my back and slid under the car. There it was.
It had fallen through the hole provided for the hood latch, landed on a half-inch wide metal strut behidn the grille, and balanced there despite all the car bouncing I had done.
After inventing a number of new names for it and probably jumping up and down, I then used it and finished the job.
I have thought of this event many times, and it encourages me to be more methodical, more thoughtful, and more calm. It was not a pretty episode.