The final episode of Friends broke a 10-year show tradition by having a different title than the rest of the episodes. Throughout its 10-year run, Friends had various traditions and running gags that became beloved by viewers. One of the biggest traditions was the title of each episode starting with "The One...". However, the series finale broke this rule and was titled "The Last One". The unique format of the episode titles began because the producers realized that the titles would not be shown in the opening credits.
By starting each title with "The One...", it made them easier for viewers to remember and discuss with their friends. Even the pilot episode originally had the title "The Pilot" before it was changed to "The One Where Monica Gets a Roommate" and "The One Where It All Began". Therefore, the series finale was the first episode in the entire series that did not follow this tradition. "The Last One" was divided into two parts and was treated as a special event. It wrapped up the storylines of all the main characters, except for Joey who continued his journey in the spinoff TV series Joey.
Although there is no official reason given for breaking the episode title rule, it could be because there was no one event in the finale that should be highlighted in the title. The most talked-about moment of the episode was Rachel getting off the plane, but including it in the title would have overshadowed the other characters' stories. The decision to break the tradition and have the title "The Last One" was, in fact, the perfect choice. It still retained a connection to the tradition by being how the audience would refer to the episode.
However, it also gave equal importance to every character's story and did not single out one event. The finale was not just about Rachel and Ross getting back together, but also about Monica and Chandler becoming parents and Phoebe finding her happy ending with her husband, Mike. By not pointing out one particular event in the title, it was fair to all the characters. "The Last One" is considered one of the best TV finales in history, and its title was perfect, even though it broke a long-standing tradition in Friends.