One of the mysteries that is in the background but potentially explosive was the appearance of Libby at critical times in the series.
She was seen as a mental patient in Hurley's day room, but Hurley had no memory of her when the tail section survivors made it to the beach camp.
She was also instrumental in getting Desmond on his epic sailboat journey. The Desmond coffee shop meeting was one of the more forced coincidences in the series. While Libby was in a coffeehouse in California, she offered to pay Desmond's bill for a caffeinated drink, as he only had British currency. Desmond jokingly asked her for $42,000 to pay for a boat. Libby asked why he needed a boat; Desmond replied that he was going to participate in a race around the world, thereby proving to Penny's father, Widmore, that he was not a coward. Libby proceeded to tell him that her husband, David, had passed away a month prior, was an avid boating fan. David had purchased a yacht, which he named the Elizabeth
after Libby herself, intending to sail in the Mediterranean. Libby
encouraged Desmond to take it, saying that it was what David would have
wanted. Desmond promised her that he would win the race in the name of
love.
This apparently was the same time and place where Desmond met Jack running up the stadium stairs. So Libby was at the epicenter of two critical meetings.
Now, some may say that Libby's role in these chance meetings with other characters prior to the island as suspicious. Was she working for someone, like Jacob or Widmore? Was she a conduit to get people to do things, such as Hurley believing in imaginary friends like "Dave," or getting Desmond out into the Pacific to perish on the island? Or was she a guardian angel type, leading an individual to their destiny?
What if Hurley's Dave, his best friend, was the person killed when Hurley went out on the party porch that collapsed because his alleged weight? It was that traumatic event that put Hurley into a mental institution. He blamed himself for causing death and pain. And his weight gain was to remove the pain and guilt of his father leaving him as a young boy.
So if Dave was killed in the overloaded porch collapse, it could be that Dave's ghost was still around Hurley. Hurley could communicate with dead people, so that is consistent with the future story lines. Dave was probably ghosting Hurley so he could a) get Hurley to realize that it was not his fault; or b) to get revenge for dying; or c) pushing Hurley to take care of his loved one.
If Hurley was devastated by losing his best friend in an accident, likewise Libby could have been traumatized by the death of her husband, David. If Libby's David was the same person as Hurley's Dave - - - what a connection! Dave's haunting Hurley at the mental hospital, getting him to try to break out and leave, could have been a means of keeping Hurley away from institutionalized Libby. But that does not explain how Libby was manipulating the other characters to the island, and once on the island, keeping Hurley from following Dave off a cliff (and certain death). Maybe Dave was haunting Libby at the same time - - - unable to let go of her, to the point where she went insane. And the only way to get over him was to move on with Hurley.
But Dave does not seem the type to be rich to have a sailboat in pricey Newport Beach. So maybe there was another David for whom Libby shared her life. There is one other known David in the series, and that was Jack's son from the sideways world . . . a boy he allegedly fathered with sideways Juliet. It would be weird and bizarre if Libby's David was Jack's after life son - - - but since time does not make logical sense in the series, anything is possible. So Libby giving a boat to Desmond to push him on his quest to sail the Pacific got Desmond to the stadium to give Jack the advice that would push him to leadership on the island and fulfill his destiny by becoming a caring father in an alternative universe.
Or, it all could be an elaborate mental fiction crazy Libby created in order to end her lonely existence by finding a sweet, gentle, introverted rich man like Hurley. But another odd point is that Hurley's live for Libby was really solidified when Libby was killed by Michael. So Hurley and Libby could only find their happiness if they were dead. (Some would say that is a sad commentary on how the main characters were actually treated by the writers.)
The Elizabeth was a vessel that carried Desmond to the island; it represented hope of escape; and it was used to ferry characters on missions around the island. But it never like the snow globe pull of the island itself. It could be symbolic of the show itself: it was an object that had great promise and purpose, but it was shipwrecked and lost at sea. It was rebuilt and served its sailors once again. But it never left the island, just like the main characters.