In the complex vagueness of LOST's mysteries, there is little congruity except about Hurley.
People universally liked Hurley. He seemed the most plausible and "real" character of the main cast.
Of all the main characters, he was thrown the most "change" to deal with during the series.
First, he was loner. His father had abandoned his family as a young boy. To compensate, he ate. He developed self-esteem issues. He would wind up in a dead end job with an abusive boss. His mother would pester him to meet girls, but Hurley was shy and self-conscious. In many ways, he is the typical young American male. His problems led to his voluntary confinement in a mental institution.
Second, when luck shines upon him (by winning the lottery), it turns into a curse. His grandfather dies; his house burns down; his father returns only to mooch off his wealth; and people around him get hurt (like the reporter dying when a meteor hits his chicken franchise. Instant wealth and fame does not help Hurley out of his shell.
Third, Hurley tries to figure out the meaning of his curse (the Numbers) and winds up on a path of personal depression. He convinces himself that he is cursed. He survives a plane crash, and he finds himself in the position of being able to run away from the curse of his lottery winnings to try to become the old Hurley. He slowly finds acceptance and friendship with his other survivors who do not know his true background.
Imagine that: Hurley being content on being a cast away. He never truly states that he wants to leave the island to rejoin his past life. He does not push to be on Michael's boat.
During the series, Hurley is in the background for most of the missions. But he is never physically attacked by the smoke monster. When he is captured by Ben's people, he is immediately released (he is not tortured like Jack, Sawyer or Kate). He sees Jacob when the Others do not. He can have full conversations with the dead. And the dead could physically slap him. And his imaginary friend Dave spoke to him on the island. Why is that?
One could assume that Hurley was never truly in danger because he controlled the dangers. The people in the LOST saga, both living and dead, were so "real" to Hurley. They were so real because Hurley imagined them all. The whole LOST universe, with its science fiction references and reoccurring continuity errors, was basically all inside the imagination of Hurley's mind.
Many people believe that there is ample evidence for the series being trapped inside the mind of a crazy person.
The Numbers that engulf Hurley's consciousness continually appear throughout the story: as the radio tower code, the part number to the Hatch, to the numbers of the candidates. If the Numbers are the constant to move the story engine forward, it is Hurley who is at the controls.
Hurley is shown escaping into fantasy settings, such as his love of strange comics and Star Wars science fiction. He has an active imagination. In the mental hospital, he can hallucinate fully functional people like Dave. Hurley's subconscious may be the heart of his crazy notions, such as the island bird calling his name, or making objects like Jacob's cabin disappear.
With all the death and destruction around him, Hurley does not get injured. He does not lose weight after months in the jungle. He maintains his appearance and attitude throughout the series.
Since Hurley was calm and relaxed at the mental institution, he would have seen and met Libby in the day room. However, on the island he did not know of her past. Was Libby another fantasy person like Dave? If so, then Libby being on the island reflects that the island is part of Hurley's mental fantasy.
When Hurley gets stressed out, he wants to return to the mental institution. In the facility, he can be left alone with his own thoughts. It is in these thoughts are his vivid dreams, including the island adventures. Hurley's mind has merged various aspects of his personality: the need for friendship, the love of games (missions), the rebellion against authority, the meekness around women, escapism, and the things in his life that he cannot change can be dealt with in his dream world.
In a dream world, anything is possible. Anything can happen. One could experience time travel. One could fall in love with Libby. One could escape the wrath of a smoke monster. One could talk to the dead. One could be a rich multimillionaire. One could be the hero.
If one seeks a simple theory of the LOST universe, no one would have to go beyond the character of Hurley to find it. Imagine the series without Hurley's presence. You cannot. He was the intersection of all the vast elements. He was the traffic control officer. And in the end, we are told that the Island was his (but in reality, it was always his fantasy island).