Yeah, I figured this might come up and I know it wasn't made clear in the fourth book and I'm planning on expanding on for the fifth book when Louis goes back to Sin to start the new Round Table. It basically happens off-panel, but Louis and Thomas have a discussion about a number of reasons why the original Round Table of King Arthur failed and one of them is a discussion of its true greatest knight - Galahad. Using Galahad as a standard or example by which knights should act, Louis decides to incorporate aspects of Galahad's character in order to make the Round Table work, one of which is that in The Once and Future King, Galahad never kills anyone. In fact, the other knights don't like him because he effectively managed to defeat all his opponents and never had to kill them, simply knock them unconscious.
Louis believes that the reason he was defeated by Varek initially is a matter of his own character - he was a violent, almost murderous individual who had polarized ideas of right and wrong and was willing to kill his enemies to prove himself right - i.e. he was stronger, therefore he was right. When Thomas saved him from himself during "The Break," he taught Louis a different approach to fighting Varek - not trying to kill him but instead to let Varek destroy himself through his own iniquity. I should probably make it a little clearer when I edit the fourth book. ^_~
Quote of the Moment: “Greetings, my friend. We are all interested in the future, for that is where you and I are going to spend the rest of our lives.” ~Criswell~