Hrishikesh Mukherjee informed his writer Gulzar to open the film in such a way that the audience knows in the first scene itself that Anand (played by Rajesh Khanna) is dead. He did not want the audience to be in a state of suspense till the end and keep guessing whether Anand will survive or not. By doing that Hrishikesh Mukherjee wanted to concentrate on the essence of the film on how Anand wants to live life fullest and make the best of the time he has.
The term "Babu Moshai" means "great gentleman." Raj Kapoor often affectionately addressed Hrishikesh Mukherjee with this term, just as Anand addresses Banerjee in the film.
Mehmood advised Amitabh Bachchan to grab a secondary role alongside the then heartthrob Rajesh Khanna in the film, saying, "All you need to do is feed off Khanna, the rest will take care of itself."
Originally, Hrishikesh Mukherjee had envisioned Shashi Kapoor, the brother of Raj Kapoor, for the role of Anand. He wanted Raj Kapoor himself, but he had just recovered from his illness and Mukherjee couldn't bear to see him die on the screen, since he had almost died in real life. In any case, Shashi Kapoor was not eager for the role, so Rajesh Khanna got it - it remains his most memorable role with Aradhana (1969) and Amar Prem (1972).
Hrishikesh Mukherjee brought back Salil Choudhury, whose career had reached a cul-de-sac in Bombay due to lack of commercial acceptance, and Yogesh, a then-forgotten lyricist. Their careers revived significantly after the film.