Isolation, or loneliness, versus group cooperation in survival, was a recurring theme on Lost. Damon Lindelof has stated, "We think it's one of the unifying themes of the show--the idea that they need each other in order to survive on the Island."

Occurrences

Season 1

• Jack told the survivors: "If we can't live together, we're gonna die alone." Portions of this phrase were quoted throughout the series, and it was referenced by the title of Season Two's finale, "Live Together, Die Alone, Part 1". ("White Rabbit")
• Sayid left the group to explore the Island and to cope with his past as a torturer. ("Solitary")
• Danielle Rousseau was found living alone in a makeshift shelter. ("Solitary")
• The raft failed to leave the Island. ("Exodus, Part 2")

Season 2

• The tailies ended their isolation from the middle section survivors. ("Abandoned")
• Charlie sang, "All alone, I try to be invincible/Together now, we can be saved." ("Fire + Water")
• Nathan was isolated in the pit created by Ana. ("The Other 48 Days")
• In a less direct scenario, Locke became isolated when he worked with his father, and Helen found out about it. The end result was Locke losing the love of his life and his father figure, leaving him alone, even though he did not wish to be.("Lockdown")
• Ben told Locke, "God doesn't know how long we've been here, John. He can't see this island any better than the rest of the world can." ("Dave")
• The Elizabeth failed to leave the Island. ("Live Together, Die Alone, Part 1")
• Desmond nearly contemplated suicide at the thought of being left alone in the Swan for an indefinite amount of time after he killed Kelvin. He read a letter by Penelope that gave him hope -- it said, "Please don't give up, Des. Because all we really need to survive is one person who truly loves us." ("Live Together, Die Alone, Part 1")

Season 3

• The Others seemed to have isolated themselves at the Barracks. ("A Tale of Two Cities")
• Sawyer was tricked into thinking he had a pacemaker implanted that could kill him and that the same would happen to Kate if he confided in her, so he was forced to stop sharing information with her. ("Every Man for Himself")
• Ben showed Sawyer that they were not on the main island where many of his friends were, but on a separate smaller island comparable to Alcatraz. He then quoted Of Mice and Men: "A guy goes nuts if he ain't got nobody. It don't make any difference who the guy is, so long as he's with you. I tell ya, I tell ya, a guy gets too lonely, and he gets sick." ("Every Man for Himself")
• Mikhail said that he preferred to live in isolation. ("Enter 77")
• Sawyer was tricked by Hurley into thinking that he would be exiled by the group for being antisocial. ("Left Behind")
• Juliet was isolated by the group when she first came back with Jack, Kate, and Sayid. ("One of Us")
• Jacob lived in a cabin in isolation. ("The Man Behind the Curtain")
  • However, it is not known if this was ever Jacob's home; Jacob was never seen in the cabin, and Ben confirmed he had never seen Jacob in the cabin. It would seem, though, Jacob lived alone in isolation bneath the statue.
• Charlie died in the Looking Glass inside the equipment room, isolated in the room from the rest of the station. ("Through the Looking Glass, Part 1")

Season 4

• Juliet told her therapist from The Others that the way she was treated like a celebrity maked her feel isolated; she corrected herself saying she feels "alone." ("The Other Woman")

Season 5

• Locke found himself alone immediately after the first time flash. ("Because You Left")
• Rose and Bernard were revealed to have been living alone in the jungle for three years following the flaming arrow attack. ("The Incident, Part 1")
• Locke was physically and emotionally isolated after failing to convince the Oceanic Six to return to island, and when he attempted suicide.