Okay, apparently it was too obscure. To clarify, my interpretation is that Tom Riddle went to that monastery, learned martial arts and how to (pretend to) lose, and once he was done, put on the glowing-red-eyes schtick and killed everybody (except his one friend) to prevent anyone else from learning what he had. He wasn't foolish to want that story spread by the one survivor - he wanted to be underestimated, to make people think he was murderously impatient when he was coldly calculating.
Rule Twelve is more general than just "kill Slytherin's Monster," it applies to all sources of power.
(The account is about halfway through Chapter 19, btw.)
OK, you were simultaneously describing, with the same text in that one paragraph, two different episodes in Tom Riddle's life. Now I get it!
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: