While Ranbir Kapoor played the title role, Priyanka Chopra was seen as autistic Jhilmil Chatterjee and her performance won her many awards. Illeana D'Cruz also featured in the romantic-comedy.
"When I went to cast Priyanka Chopra, I realised that I could not see her as my character. I told her that I was not sure and that we should have a three-day workshop, " said Basu.
The director was speaking at an acting workshop - 100 years of Indian Cinema: An actor Prepares" - held on the second day of the ongoing 14th International Indian Film Academy (IIFA) awards and weekend here. It started Thursday.
He further said: "The first day of the workshop was tough as Priyanka was very formal. I asked her to hold my collar and shout abuses at me, this loosened her up a lot."
"I told her to see the world from my character's eyes and everything will fall into place. She just had to be there in the moment, " he added.
How do you usually cast for your films?
"I need to have clarity in my mind. As long as there is clarity, I can choose my cast in one go, " he said.
The director, who has directed films like "Barfi!", "Life in a...Metro" and "Gangster - A Love Story", describes the current lot of actors as easy-going.
"All the actors of our generation are easy-going. But all of them are different. Hrithik Roshan is more reserved, while Ranbir and I became great friends as we have the same likes and dislikes. You have to balance everything as a director, " he said.