"Writing is like the spine of a film and the entire film stands on that 'spine'. When you stand in front of a person, you don't see the spine, you see the entire person. People will always look at the face but when you look deep into it, you realise how strong the spine is," Iyengar told IANS.
Similarly when people watch a movie, they immediately see what attracts them the most - actors, locations, and songs, he said and added: "But the only movies that survive the test of time are the ones with strong story and writing."
However, giving writers their due doesn't necessarily mean that they should hog limelight at movie promotions, Iyengar said. He believes "everybody has a part to play in the making of a movie".
"Whether they are part of a promotion or not, whether they are taken everywhere and their pictures are published in the newspaper or not, people within the business and people who need to know, know who has done what," he added.
Knowledge quotient should be bigger for writers irrespective of the subject that they are writing upon.
"For a writer, it is very essential to have a world view. Even if you are writing the smallest thing in the world, you must understand its context in the larger world. Unless you understand the context of any object, any character in the larger world, you won't be able to tell any story with the kind of objectivity that is required," Iyengar said.
While "Heroine" is an edgy, serious movie about an actress's off-screen life, "SOTY" is a light-hearted youth drama.
"Both the films were shooting simultaneously and I was writing for them simultaneously. There were times I felt schizophrenic, running from one side to another. One side of me had to be very light and frivolous, while the other had to be dark and profound," he said.
As time is changing fast, it was important for him to study youth's life for "SOTY", which is releasing Oct 19.
"I definitely needed to do that because I was younger many years ago and since then the world has changed. There is a lot more accessibility to other parts of the world than when I was younger," Iyengar said.
"The language changes, the grammar changes, the thoughts evolve. For me, one of the greatest support on 'SOTY' was Karan Johar. He knew what he wanted and how he wanted to project youngsters."
Talking about "Heroine", coming out Sep 21, he said: "It's just that both me and Madhur have been part of the industry for almost 20 years and we have a certain sense of the film industry...Madhur has a certain sensibility with which he works, which is always more sensational and bold. I don't think he had any guidelines in mind."