Damon & Carlton have continued stated over the years that they have known where the show was going to go from the beginning, and they always had one ending in mind.
I always thought that wasn't the case myself, it's clear throughout seasons 1 and 2 that the show has no idea what it is or where it's going.
Recently, the creator for series Defying Gravity quoted both Damon and Carlton as saying they "haven't a clue" where Lost was going during season 1.
So why do they keep saying they had the ending in mind when it's obvious they didn't?
Been meaning to do this, but here's another interview where they blatantly state the entire thing has never been fully planned out, despite what is reported and stated by the network.