- The writers had wildly different plans for many of the central characters. The most famous of these is the by now well-known early plan to have Jack killed by the monster in the middle of the pilot episode. Casting footage on the first season DVD shows just how differently the show might have evolved, with Matthew Fox reading as a much slicker version of Sawyer, Yunjin Kim (Sun) reading for Kate, and multiple mentions of Kate's husband, who was in the tail section. Furthermore, Jack was to be played by a "name" actor (Michael Keaton was specifically mentioned) before being offed and Nikki and Paulo were intended to become major characters. Specifically, "Exposé" was planned to be solely Nikki-centric and follow her time on the show... and only reveal at the end that the absurd stripper plot was part of a show. Luckily, they were killed off and, thankfully, this was quietly dropped.
- Charlotte was originally meant to be an American and the role was offered to Kristen Bell, but she rejected it for a role on Heroes. So it was changed when British actress Rebecca Madder was cast. This has lead to a (implausible) theory held by some that she was meant to be revealed as Annie (given her link to DHARMA), but since Annie was American this was quietly dropped later on.
- Jon Hamm auditioned for Jack.
- Forest Whitaker was offered the role of Sawyer, but he was busy directing First Daughter.
- Lance Reddick was offered the role of Mr. Eko, had to drop out due to his role on The Wire.
- Jennifer Jason Leigh was considered for Libby, but it never got past the producers asking her.
- The original mythology was going to be much more sci-fi oriented.
- In the event that the show be Cut Short partway through the first season, then plan was to reveal the island to be in The Bermuda Triangle.
- Mr Eko was meant to be one of the most important characters on the show, with a arc that would cover the rest of the series. Then the actor left. Sayid's season 5 and 6 arc was intended for Eko, although that leaves the question as to what Sayid's original storyline would have been.
- He was originally to be named "Emeka".
- Likewise, Ilana was meant to have a big part in the final season-in fact, she was going to be Jacob's daughter! But this was cut and scenes were refilmed when they decided they didn't have enough time for this. This explains her promotion to regular, despite not having any development or much importance outside of "Dr Linus" and her abrupt death and absence from the finale.
- The original name of Charlie's band was "The Petting Zoo". This had to be changed, however, when it transpired that there really is a band called "The Petting Zoo".
- In original drafts for the show, Rousseau's team of scientists were studying time. The network told the writers not to include it in the show, in case the viewers would think it too science fiction and stop watching.
- The original idea for the Others was that they would be a group of feral jungle dwellers. This was later changed when they were re-imagined as technically advanced and sophisticated people, who only use a disguise of feral jungle dwellers to mislead new arrivals on the Island.
- Caesar was meant to have a regular, and fairly major, role in the final season. But the actor turned down more Lost in favor of G.I. Joe, so Caesar's abrupt death stuck and his character became an unintentional red herring.
- Daniel, Charlotte and Miles were originally planned as guest stars who would last eight episodes, tops. Thanks to how awesomely "Confirmed Dead" turned out, they were promoted to regulars for the rest of season 4 and beyond; while Charlotte was killed off early in season 5 and Daniel was killed off at the end of the season, Miles is still around and Frank has also made the jump to regular for season 6.
- After the idea of the reset was introduced, the producers considered season 6 both featuring no reset/alternate timeline of any kind, or a complete reset. After deciding both approaches were deficient, they decided to do both. In fact, they decided to both "do both" and "not do both" by having the alternate timeline in fact be a waiting room for the afterlife rather than an actual alternate timeline, while still having it take place in a what-if-the-plane-never-crashed scenario.
- There was a planned subplot, revealed at Comic Con, that had the DHARMA researchers know that a Stable Time Loop was going on, and that they would perish. It was dropped, due to time constraints and new writers.
- The elements in the tie-in video game, the alternate reality games, and a teaser at Comic-Con where one of the DHARMA researches stated that they knew the events on the island were to die, thanks to the nature of time on the island, were all dumped.
- The climactic battle in the series finale was going to happen during a volcanic eruption, which was planned early enough for a passing mention of volcanic activity in Season 3. ABC ultimately refused to okay the budget for it, which Lindeloff and Cuse quickly realized was a good thing as the lava battle from Revenge of the Sith would be fresh in everyone's minds and they never could have measured up to it.
- Mr. Eko was originally supposed to appear in the series' finale, but a deal could not be worked out.
What Could Have Been / Lost