The Watchman's Rounds
A night watchman guarded a warehouse.
He didn't wait for trouble. Each hour, he walked the perimeter, checked the locks, tested the lanterns.
One night, he found a lock broken — not forced, just worn through. He replaced it before dawn.
The warehouse down the street had a watchman who only responded to alarms. By the time he noticed the broken lock, the thieves had already come.