Struggling
and suffering are the essence of a life worth living. If you're not
pushing yourself beyond the comfort zone, if you're not demanding more
from yourself - expanding and learning as you go - you're choosing a
numb existence. You're denying yourself an extraordinary trip.
— Dean Karnazes
Perhaps the series was merely a journey for otherwise dull, boring, lonely people. The common trait of the main characters was unhappiness. They were all in a rut; their futures looked bleak; and they have relationship issues.
If the island was a proving ground for a life worth living, then it was probably a successful intervention.
Putting a collection of diverse people into a savage, unknown, mysterious and dangerous island with no chance of rescue is going beyond the comfort zone of all the characters.
In order to survive, each character had to go beyond their routine. They had to demand more from their inner self - - - change or adapt to the new circumstances. They had to make decisions and not loiter on their past routines. They had to learn to live together, to trust each other, and to value the security that various levels of friendship would provide. It was the personal expansion of each character that was the most noticeable aspect of the show.
For example, Hurley was a shy, self-doubting individual who never wanted to take risks for fear of failure. He had mental issues and blamed himself for bad things happening to other people. He was most comfortable hiding away in a mental institution, away from the normal stresses and anxieties of daily life.
Jack was a brilliant spinal surgeon, but he led a tortured monk-like existence outside of work. His relationship with his father was an anchor around his neck. He could not handle relationships with women; his marriage fell apart due to his own illogical behavior.
Sawyer was a charming but devious con artist. His noble cause to find his parents killer turned him into the same person that he hated as a child. As a drifter, he kept no lasting personal relationships. He was a loner, and that caused him to be bitter - - - to lash out at others because the only person he could trust was himself.
Kate was also a loner. She was popular, a tom boy who learned early that she could manipulate men to do what she wanted them to do for her. But she was troubled; she did not understand the big picture. She had no direction or big dreams. She lashed out for her mother's attention, but she was shocked when her mother turned on her. Kate's survival mechanism was to run, escape and hide from her problems.
Sayid was brought up in a stable family, but the war changed him into a dark soldier. He was recruited and trained as a torturer, who turned on his childhood friends. He would become a loner by his own actions, fearful that he would revert to being a killer. As such, he had no close friends. He kept to himself because his instincts made him believe only in himself and to distrust others.
From each viewer's own observations of the characters, the amount of change in their personality is apparent. If the show was all about character development, then the main characters did have to cope with the insane circumstances thrown at them, to trust themselves and others, in order to fully experience life at its best and at its worst.