"Kyun! How Gaya Na..." is a simple story about love and life. But then again who has said that love and life are all that simple...??? Diya Malhotra meets Arjun Khanna under unusual circumstances. It proves to be a perfect beginning to a memorable relationship. Once she arrives in Mumbai she realizes that she will be staying in the same house as Arjun. The ground is thus set for events that were always meant to be. The friendship that develops between Diya and Arjun, spiced up with their opposing views on love and marriage, form the heart of the film.