Is there a law .....?

So I worked for hours making a part for my throttle linkage mount. I was holding it with pliers and sanding it on a belt sander to finish it up when it flew away. Do you think I could find it? No!
This has happened before, working with grinders, wire brush wheels, and compressed air nozzles.
There must be a law that says that this will happen. What's the law?