I was screwing together an electronics enclosure today, and I dropped a screw.
Figure 1: Dastardly slippery things
I peered around on the floor to find where it went, and within arm's reach came up with two screws of roughly the same size and shape. Upon further inspection, neither of them were my screw.
But, one of them worked anyway! I'll leave my dropped fastener wherever it landed, perhaps for the next researcher to discover....