Trama

Naina, an introverted, perpetually depressed girl's life changes when she meets Aman. But Aman has a secret of his own which changes their lives forever. Embroiled in all this is Rohit, Naina's best friend who conceals his love for her.

The film's female lead, Naina (Preity Zinta) narrates the story. Her father had committed suicide years ago which left a deep impact on her heart. Her family is dysfunctional since her mother and grandmother just cannot stop arguing. But when Aman (Shahrukh Khan) arrives next door, the whole gloomy conditions change. Aman infuses life in skeptical and overtly serious Naina, and she falls in love with him. But Aman knows that he cannot marry Naina because of a secret which he cannot divulge to her. So he intends upon setting her up with her best pal Rohit (Saif Ali Khan).—Soumitra

Naina is a very serious girl with a very serious life. But one day, her soul is awakened by the happy-go-lucky Aman, who teaches her that life is meant to be lived. Naturally, she falls in love with him. But Aman is harboring a secret that keeps him from reciprocating Naina's love. But he cannot stand having her live a life without love, so he sets off on a mission to fill her life with someone else's love - someone she already knows....—anna bo banna

Naina and Rohit are best friends. When Aman comes into their lives, their worlds are turned upside down. Aman tries to play matchmaker between them and succeeds as Rohit falls for Naina. However, Naina falls in love with Aman, who although also in love with her, rejects her love. Meanwhile, Aman goes around fixing Naina's family problems.—Moneymaker

Naina Kapur is the eldest of three and currently doing an MBA course in New York City. Her coursemate Rohit is a playboy wannabe who fails more than he succeeds, and the two befriend each other since she's one of the few women he doesn't plan to court. Naina lives with her mother and her paternal grandmother who, in essence, is your stereotypical mother-in-law. Not everything is going smoothly for the family. Their restaurant business is constantly in the red and family squabbles between the two in-laws are constant. However, the Kapur family still maintains their status quo, even if the children are unhappy about it. Enter Naina's new neighbour, Aman Mathur - a charismatic busybody who gets into everyone's face and then gets away with it. He brings a new life to the neighbourhood and slowly but surely begins to change the lives of everyone around him. He pushes people to become the best that they can be, and even gets Rohit spurred on enough to court Naina seriously. That is, until he realises that he's falling hard for Naina as well. And to complicate matters, Naina has also fallen for him.—Peter Lin

Naina Catherine Kapur (Preity Zinta) is a pessimistic, uptight Punjabi American MBA student who lives in New York City with her widowed mother Jennifer, a Punjabi Christian, disabled brother Shiv, adopted sister Jia and paternal grandmother Lajjo, a Punjabi Sikh. Jennifer runs an unsuccessful cafe with her neighbor, Jaswinder "Jazz" Kapoor (Lillete Dubey). The restaurant Jennifer operates is faltering and Jennifer is struggling to pay rent on the property as well as the bank loan.

Naina's father committed suicide when she needed him the most, leaving her mother Jennifer (Jaya Bachchan) to raise their two young children Shiv (Atith Naik) & Jia (Jhanak Shukla) all alone.

Furthermore, Naina's paternal grandmother, Lajjo (Sushma Seth), blames Jennifer for the suicide and refuses to accept Jia, a six-year-old girl whom Jennifer adopted, as her granddaughter, blaming her for bringing bad luck to the family. Lajjo wants Naina to get married to a Sardar. She has sisters Vimmo (Kamini Khanna) and Kammo (Shoma Anand), who are always with her. Uncle Chaddha (Dara Singh) has a crush on Lajjo. Lajjo has Naina listed on a matrimonial site to look for suitable matches, which irritates her.

Naina has to put up with the daily fights that take place in the house as a result. The only bright spot in her life is the toiling and tolerant Jennifer. Naina has two best friends: her classmate, Rohit Patel (Saif Ali Khan), a Gujarati American, and Jaspreet "Sweetu" Kapoor (Delnaaz Paul), Jazz's sister. Rohit is the son of KarsanBhai (Satish Shah) and SalraBen (Ketki Dave), who run a Dhokla based fast food chain in the country. Rohit maintains a black diary which he never shares with anyone. Rohit is a flirt, but a good guy at heart.

Aman Mathur (Shahrukh Khan) arrives in Naina's neighborhood and soon changes everything. Noticing the sadness of his new neighbors, he intervenes. His well-meaning interference in their activities, his revival of their financial condition, and his general optimism, soon change their lives for the better. He suggests that they change the cafe to an Indian restaurant and its success alleviates their financial burdens. Although Naina is initially reluctant to enjoy Aman's presence as others do and is irritated by his extroverted, overly enthusiastic attitude, she grows to like him and eventually falls in love with him.

Rohit also falls in love with Naina and asks Aman's help in expressing his feelings. Naina tells Rohit there is something she must say to him, leading him to think that she reciprocates his feelings. Naina reveals she is in love with Aman instead. Shaken, Rohit calls Aman to tell him what has happened.

Naina goes to Aman's house where, to stop her from confessing her feelings to him, Aman tells her that he is married to a woman named Priya (Sonali Bendre), who is actually his doctor. Heartbroken, she leaves. Aman, it is revealed, is dying of a severe condition that is progressively weakening his heart. Knowing that his lifespan is limited, he goes through life facilitating friendships and courtship, and urging people to enjoy themselves in the present moment since "Tomorrow might never come".

His excursions into such altruism, eventually leads him to sacrifice his love for Naina and instead play matchmaker between her and Rohit. He is not actually married. Priya is his childhood friend and doctor. Aman vows to bring Naina and Rohit together before he dies. He believes that Rohit will be able to provide for her better than he can. After a few weeks of courtship, Naina starts to like Rohit as more than just a friend. However, when she finds out that Aman has been helping Rohit to woo her, she gets very angry at them both. Naina chides Aman for trying to ruin her friendship with Rohit. Aman takes out Rohit's diary and confesses his feelings for Naina, saying they are Rohit's. Naina forgives Aman and Rohit. Rohit proposes to Naina, and she accepts.

Lajjo and Jennifer have a serious fight regarding Jia, who calls on Aman for help. The tension within Naina's family also stops when Aman, after accidentally intercepting a personal letter addressed to Jennifer, reveals that Jia is Naina's half-sister through their father's extramarital affair. When Jia's biological mother refused to accept her, Jennifer adopted her. Jennifer's selfless acceptance of her husband's infidelity is what led to his suicide. Lajjo finally accepts Jia, and the now-united family wholeheartedly prepare for Rohit and Naina's wedding. Naina gains closure after learning the truth about her father's death.

Aman's health deteriorates. At the engagement party of Rohit and Naina, an episode of intense excitement nearly kills him. Naina encounters Priya at a jewelry store, whom she recognizes as Aman's wife. She introduces herself and her husband, Abhay, who reveals the truth about Aman. Shocked, Naina realizes that Aman has sacrificed his love for her and leaves the mall in an emotional frenzy. Priya calls up Aman and informs him about what happened. Aman leaves the hospital and meets a frustrated Rohit, who asks why he and not Aman should marry Naina. Aman urges Rohit to marry Naina as a sign of respect for his dying wish to see Naina happy.

Naina goes to see Aman, and although he defiantly refuses to admit his true feelings, she finally understands that he loves her deeply as well.

Aman convinces Naina to get married to Rohit anyway, because he knew he won't live much longer and doesn't want to leave her alone and heartbroken after his death. She accepts and shortly after Rohit and Naina marry. Aman on his death bed, makes Rohit promise him that Rohit will let him have Naina in the next life (heaven). Aman in a hospital room eventually slips away in his sleep, with Rohit by his side and Naina watching through the door.

Twenty years later, an older Naina relates the story of Aman's selfless love to a grown Jia and how he was her first and true love and that she nor Rohit can ever forget him and neither can Jia. It is seen that she and Rohit now have a daughter of their own.