Is it round?
Maybe it fell on the floor and rolled clear across the room.
Is it magnetic?
Could be stuck to the bottom of something. You lift the other thing up and don't see the missing piece because it's stuck to bottom of the thing you're holding.
Is it the same color as some other thing?
It could be on the other thing but blending in so you don't see it while looking right at it.
Is it small? Have you checked your pockets? Did it fall into the gap between your ankle and shoe?
Did you go to the break room or restroom or have you been by the work bench 100% of the time? Is it in the break room or bathroom?
There's prolly some other obvious thing but I'm sleepy and that's all the guesses I can come up with now.
It's not round, it's big and flat
It is magnetic, but so is the piece it connects to.
It's a different color from the other thing(s)
It is not small.
It's in my home. No one else is there.
I think it's just gone.