Many promises are made on Lost; some are fulfilled, while others are not.
This article is an attempt to chronicle many of the noteworthy promises made during key moments in the show.

Season 1Edit

Jack promises Rose that he'll keep her company.

• Jack promised Rose that he would be with her until Bernard came back. ("Pilot, Part 1") He fulfilled his promise since Rose said he didn't have to be with her all the time.
• Charlie promised to look after Claire. ("Raised by Another") He fulfilled his promise by protecting her after she escaped Ethan and by killing Ethan to protect her.
• Ana Lucia promised to share a drink with Jack on the plane. ("Exodus, Part 1") She was unable to fulfill this promise due to the plane crash.
• Shannon promised Walt that she would look after Vincent. ("Exodus, Part 1") She fulfilled the promise, caring for the dog until she was killed.

Season 2Edit

• Jack promised Sarah he would fix her. ("Man of Science, Man of Faith") Jack succeeded, despite believing that he failed.
• Jack promised everyone still alive that the sun would come up in 3 hours and they would all still be alive to see that happen. ("Man of Science, Man of Faith")

Season 3Edit

• Kate promised Jack to never go back for him. ("I Do") She broke her promise almost immediately after, taking Locke, Sayid, and Rousseau to the Barracks in search of Jack.
• Ben promised Juliet that he would let her go home if he survived the spinal surgery. ("I Do") He intended to follow through on the promise, but Locke destroyed the Galaga before he could.
• Ben promised Juliet that if she went to the island to help with the pregnancy issues, he would heal her sister, who had cancer. He kept his promise and her sister was healed.

Season 4Edit

• Penny promised Desmond she would answer the phone on Christmas Eve 2004. ("The Constant")
• Desmond promised to call Penny on Christmas eve 2004. ("The Constant")
  • They both followed through on their promises, which saved Desmond from dying due to temporal displacement.
• Keamy promised to kill Alex Rousseau if Ben didn't surrender. ("The Shape of Things to Come") When Ben still refused, Keamy made good on the threat and shot Alex before Ben's eyes.
• Ben promised Charles that he would kill Penny. ("The Shape of Things to Come") He failed to fulfill this promise, as he was disheartened at the sight of Penny's son, and brutally beaten by Desmond.

Season 5Edit

Locke shows Ben Jin's wedding ring. ("This Place Is Death")

• Locke promised to not bring Sun back to the island. ("This Place Is Death") Locke himself never contacted Sun, although his actions led to Ben bringing her back anyway.
• Ben promised the Man in Black in the form of Alex that he would do whatever "John Locke" (unbeknownst to him, actually the Man in Black) said. ("Dead Is Dead") Ben kept his word, killing Jacob on the Man in Black's order, although he ceased obeying him after learning the Man's true nature.
• The Man in Black in the form of Locke promised Sun to do all he could to reunite her with Jin. He tried to fulfill this promise, but Sun refused to follow him out of mistrust and fear.
• Kate promised Jacob she would not steal again. ("The Incident, Part 1") She did not keep her word and stole repeatedly throughout her life.
• James promised not to finish his letter to Sawyer. ("The Incident, Part 1") James did not keep the promise, and finished the letter, finally delivering it in 2004.

Season 6Edit

• Ben promised Alex that he wouldn't say anything about principal Reynolds and the school nurse. He broke his promise and tried to blackmail Reynolds about the affair. ("Dr. Linus")
• Jack promised to get Sun and Jin on the plane and off the island. ("The Package") He ultimately failed to keep the promise, as the Man in Black destroyed the submarine they were traveling on, and Sun and Jin were killed. ("The Candidate")
• Desmond promised Penny that he would never leave her again, yet he was brought back to the Island by force. ("The Package")
• Kate promised Claire that Claire would come back to Aaron to raise him. ("The Last Recruit")
• Jin promised Sun that he would never leave her again. ("The Candidate")
• The Man in Black promised Charles Widmore he wouldn't kill Penelope if Widmore revealed why he brought Desmond back to the island. ("What They Died For")
• Kate promised Claire that everything would be alright when she delivered Aaron. ("The End")