"Kyun! Ho Gaya Na.." is a situational romantic comedy

Diya Malhotra (played by Asihwarya Rai) is an idealistic, sensitive girl whose childhood was spent in the coffee plantation town of Coorg. Malhotra (Played by Tinnu Anand) single - handedly brought up Diya, after his wife passed away.

Malhotra has a dear friend Raj Chauhan (Uncle played by Amitabh Bachchan), a confirmed bachelor who has dedicated his life to a small orphanage he has in his home. Diya has been involved with the work exam she comes to Mumbai.

In unusual circumstances, she meets Arjun Khanna (played by Vivek Oberoi). Arjun is a seemingly free spirited, fun loving, adventurous guy. Once she arrives in Mumbai they realize that they will be staying in the same house since Arjun's parents (Played by Om Puri & Rati Agnihotri) are friends of Malhotra's.

The friendship that develops between Diya and Arjun and consequently their opposing views on love and marriage are at the heart of the film.

It is a simple story about love and life.