Here's what I've been thinking, though it is a bit fuzzy around the edges...
There was only one timeline until the detonation of Jughead caused it to split. Think of the letter "Y".
On one side of the split, the one we're calling the Sideways, the scale seems to be tilted toward the white/Jacob. It is indeed bittersweet as Alvin said, although that is only because we have awareness of the other timeline. If we didn't have that special knowledge, the lives of the Losties would seem mostly pretty good to us.
On the other side of the split, the scale tilts to the dark/MIB. This is the timeline we call the "real" one. The one in which flight 815 does crash. The island experiences of the Losties have been pretty awful overall, with bright spots few and far between. What we saw of their pre-crash lives in this timeline (through the flashbacks) was also rather dark and full of turmoil.
What we saw in this episode ("Happily Ever After") was a lot of the universe attempting to course correct. These two split timelines must be re-joined for balance to be restored. And that's where Desmond comes in.
I saw a comment on a Lost forum that summed it up beautifully - Desmond has to prevent it from ever happening and fix it after the fact at the same time. And he's the only one who can because the rules don't apply to him.
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With only five episodes left, I've decided to stop watching each week and wait until Mr. Webby gets caught up. That way we can experience the end of the series together. You could say I'm joining our separate viewing timelines into one.
We are already halfway through season 3 in our watching together which means I'll probably see the series end about a month after the rest of you so I'll have to avoid this thread until then starting next Tuesday.
Here's hoping the end will be satisfying and we'll all be happy to have invested our time in watching and thinking about this show. We will know soon.
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