Rose and Bernard.
At some point during season 6, our Losties will have to make a choice. A choice which determines which side they will fight in the coming war. Who be allied with Jacob, and who will go with MIB?
Here is my guess on how this may happen. I think there'll come a moment is Lost where each character will be presented with this choice, and the way it will work is that they will each pick a stone. A white stone allies them with Jacob. And a black with MIB. Neither choice is right or wrong, good or bad. What if this choice comes to Rose and Bernard seperately, and they pick different stones? Obviously, they won't want to be apart so they will solve this problem by deciding NOT to choose. They will be the only characters who decide not to ally themsleves with one side or another. And so they'll be cast out, forced to live alone. And they'll choose the Caves as their final home.
So, that's my theory. How they end up 50 years ago, I don't know. Any ideas?