This is the first time ever in all of Lost that I have been right about anything. And I'm extatic about it.
I had stated before in a blog that Desmond had become conscience of himself in both realities (much like Eloise) and that was why he is the key to this.
Last nights episode "Everybody Loves Hugo" just validated it for me. When Ben asked why he was at the school, Desmond said he was looking for a school for his son Charlie. However; in that reality Desmond has no family let alone a child, yet he knew that he had a son and his name is Charlie.
This will probably be the only thing I am ever right about (it's taken me 6 seasons for this first one) so I just wanted to scream it from the rooftops. Also, I understand that this was a simple thing to figure out and others probably did as well, but I don't see why they aren't cheering at their genius either.