Glass On the Floor

I don't know why this is the case, but it's certainly true.

If you break glass on the floor, you can make many passes over the same area with the broom. You can then get down on hands and knees and eye every square inch of space to make sure you haven't missed any. You can make another pass with a damp rag to get tiny tiny pieces that you might have missed.

No matter what, after a day or so passes, you will find a big giant piece, at least an inch long, sitting right in the middle of the floor where someone is likely to step.