In a kingdom, the King did not allow any citizen to visit the world outside. Also only a person with a proper paperwork was allowed to enter or he was sent back. A wooden bridge was the only connection between the kingdom and the rest of the world.
The king had appointed a sharpshooter who would check the bridge every five minutes for escapees. After checking, he would go back to his hut and return exactly after five minutes again. You can't cross the bridge in less than 9 minutes, so the sharpshooter would be guaranteed to catch anyone trying to make a break for the other side.
A merchant who was a citizen of the kingdom was able to cross the bridge and escape the kingdom without harming the shooter.