After a long search for a misplaced item: "Eeh! It's always in the very last place you look."

"Of course it is. Once you've found it, you stop looking.
"Tell you what to do next time you lose something - after you've found it, keep on looking for a bit, then it won't be in the last place you look."

The penny's never dropped with my ma-in-law. She still says it every time.