It’s something that Miles has been trying to explain to Jack, Kate and Hurley since they arrived in 1977, but when Dan returned in “The Variable” he was able to explain it a little clearer for them (albeit in an crazy guy kind of way). What did he explain? Put simply, and this is just how I understand it, for the losties 1977 is their present (meaning they can die), for Dharma and the hostiles 1977 is their past (so in theory if they were still alive in 2007 they can’t die…yet).
However, and this is where even I get a little confused, those on the island that encounter the losties during that time in their past (both 1954 and 1977) still have memories of their meetings in 2007. For example, Charles Widmore tell Locke that he met him when he was just 17, yet Locke hasn’t aged a day since then. Locke tells him that its only been four days since they met, despite the meeting taking place in 1954. I’m not entirely sure how this works, is it similar to what Desmond experienced where he just woke up one day with this new memory. In other words, when did Charles remember remembering meeting Locke?
Then in “The Variable” Eloise is telling Charles that she had to send Dan back to the island knowing full well what would happen to him. She knows, because she remembers. How it is that she knows what happens to Dan on the island before she shoots him after she sends him to the island I’m still not sure (and yes, I’m aware the sentence didn’t make much sense). I can work it out in my mind, but couldn’t explain it in words if my life depended on it.
So, everything that the losties are doing in their “present” always happened in the hostiles past, it wasn’t necessarily the losties doing it but it did happen, for example Ben was probably always shot, and always healed by the hostiles, but in circumstances that didn’t involve the losties. Make sense? No? Didn’t think so.
Dan’s plan was based on his theory that he’d worked out the important ‘variables’ in the complex equation of time, and that these ‘variables’ are the people (not sure if he just meant the losties, or people in general). These people have free will etc etc and should be able to think for themselves, despite what they know, and be able to alter what happens in their future (in the case of the losties). But so far almost everything we’ve seen has really pointed towards time “course-correcting” no matter what the losties or anyone else does. The only thing that went against this was when Dan knocked on the hatch door and told Desmond to go and find Eloise, Des awoke with his ‘new’ memory of Dan that he seemingly didn’t have before.