I’m still listening to Half-Blood Prince.  (Don’t worry; I’m nearly done. I only have four chapters left, which I’ll finish tomorrow at work.)  Anyway, I had another realization while listening to “The Cave” (chapter 26).

While Dumbledore’s drinking the potion in the basin with the supposed Horcrux, there are a few protests that come from him:

“It’s all my fault, all my fault.”

“Don’t hurt them, don’t hurt them, please, please, it’s my fault, hurt me instead.”

“Please, please, please, no … not that, not that, I’ll do anything.”

Without reading Deathly Hallows, this may just seem like standard protests caused by the potion.  However, now having read Deathly Hallows, I think it becomes evident why Dumbledore says the things he does.  We learn a lot about Dumbledore’s background and, more particularly, his family.  I think this has something to do with them and how the events played out with his sister’s death or, even possibly, with his father’s arrest because of torturing those Muggle boys.  However, I can’t be positive until I listen to Deathly Hallows again as I don’t remember all the details very well.  Afterall, the only time I’ve read the book is when it was first released almost two years ago.

Updated: I just got to the point in the book when Harry tells Aberforth about Dumbledore’s experience drinking the potion.  And, Harry says as much just like Ashley said in the comments. ;) This isn’t as much of a revelation as me just realizing what it’s in reference to as I listened to it in Half-Blood Prince rather than waiting for Harry to say something in Deathly Hallows.