Was The Island All In Jack's Head? by A.Donnici

This theory will only make sense to those who have watched all 6 seasons:

When we first met Jack in season one, he was a doctor with an alcoholic father and some "daddy issues". As we learned more about his background, we started to learn about his relationship and commitment issues, along with suicidal tendencies and deep regret for mistakes made, often made in the operating room.

He was going through a lot, so while the island was not exactly ideal, it gave him a place to work through some stuff.

I think that each person represented a different part of his personality. For example Kate could have been the part of him that wanted to be strong and kind, but couldn't let go of his past. John Locke could have been the part of him that wanted to stop being told what or how to do things, and was just downright angry. Shannon could have been the part of him that wanted to be taken care of, and so on. As he worked through different issues and overcame challenges on the island, the "parts of him" started to die. When he realized that his father was kind of at the center of everything, the island jack died, because he had finished what needed to be done, and alternate Jack met up at the church with everybody else. I believe that the realization that Jack was dead and going to the church was a transition from a purgatory of sorts, and that after the church was heaven. The island was his dying brain making sense of what was happening, and the other places and adventures were a way of working through his problems. At the end when it was between MIB and Jacob (Good/Bad) He had a hard decision and realized that he needed to choose to be the guardian of the island. When he did even though he would lose everybody close to him (even though they were parts of him) he was ready to move on. So in conclusion, each character was a part of him. When he worked through the problems represented by that person, they would die. As it narrowed down to the harder stuff ( Oceanic 6) he had harder decisions. When he made the right choices and worked through his problems, he was alone, but could move on to heaven or whatever was next