This book is proof that Dumbledore intervened to make Lily Evans distrust Snape, who was the friend she is referring to. Snape whose entire existence is based upon his love for Lily had it taken away from him by Dumbledore. Quite a terrible secret indeed, but until you know that you think that Dumbledore just snuck into the girl's dorms to mess with their mind.
Where are you getting this? What makes you think he intervened to make her distrust Snape, and why do you think that's the reason things didn't work out with Snape and Lily? I don't see this from the chapter.
Also, what's the deal with Fawkes and the evil parents and him running away?
I see you already replied to the post that explains this position.
Dumbledore said the textbook contains a terrible secret. Telling a teenager how to make her sister magically pretty in a dangerous way is bad, but is it terrible?
So there's this theory that the terrible secret is that Dumbledore screwed Snape. You think that's wrong, but do you have an alternate suggestion for a terrible secret that has already been shown to the readers other than the Pretty, Pretty Potion of Doom?
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author's Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
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, eight, nine, ten.
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: