Jon W,
The best description I've found so far is:
"Origin
In The Elder Scrolls V: Skyrim, the town guard non-player characters (NPCs) have several stock lines they will repeat when the player walks near them, including a bewildered statement about “curved swords”, a patronizing statement about “sweetroll” theft, and the melancholy confession “I used to be an adventurer like you, then I took an arrow in the knee.” The restating of such a specific story over and over again by so many different guards caused it to be noticed by players, who then proceeded to post about it in gaming forums and image boards. Along with the game itself, the video below helps give the idea that almost every guard in Skyrim became a guard due to the life altering results of receiving an arrow to the knee."
Sums it up pretty well I think!
