You were the youngest Winchester. You were not meant to be any kind of vessel, but the one true witness to the apocalypse. And by that you'd remember the fight between Michael and Lucifer and recite it and then be killed by the angels. That is what was supposed to happen, but after the whole stopping the apocalypse thing, the angels allowed you to live.

So, you went about mostly being normal until Sam came around, apparently freed from the cage, and sometimes, you'd just sit and repeat details about the fight Lucifer and Micheal had that ended with them in the cage.

Sam watched you did this, staring off into space as you spoke almost robotically. He didn't feel concerned- well, he didn't feel much of anything.