Season 1: Plane goes boom so people can meet eachother.
Season 2: Hatch goes boom so we can learn about history of island.
Season 3: Glass goes boom so Charlie dies giving final message of warning about the rescue team.
Season 4: Bomb goes boom so destroy freighter trapping other people on island.
Season 5: Bomb goes boom so they can try and avoid everything. Doesn't work.
Season 6: Plane DOESN'T go boom so people can go home, and live their lives while others choose to stay and make sure island doesn't go boom.