Filmmaker Harish Shankar, best known for delivering blockbuster Telugu films such as "Gabbar Singh" and "Subramanyam For Sale", believes it's really challenging to make a good commercial film."Writing and making commercial cinema is very challenging. You need to be sure of what will work with the masses and what doesn't. Every second needs to be written in a way that it appeals to the audience," Harish told IANS.His latest film "Duvvada Jagannadham" aka "DJ", starring Allu Arjun in the lead, is slated for release on Friday.Harish said "DJ" pushed him as a writer and director within the commercial space."It changed the way how the template of commercial cinema is treated. In most commercial films, when we reach the climax we know the hero will emerge victorious. We know that it will end with an action bang. The climax of 'DJ' will surprise audiences," he said."As a writer, I have treated the dialogues differently and have not relied solely on punch lines. Also, in commercial cinema, the focus is usually on the hero. In 'DJ', I have shifted focus on other key characters as well and they all have shined in their roles," he added.On working with Arjun, with whom he has teamed up for the first time, Harish said it was "inspiring".Arjun plays a Brahmin cook in the film, which also stars Pooja Hegde."His hard work is very inspiring and it in turn motivated me to push harder. After I told him about his character, he started interacting with Brahmin priests and cooks. We shot for 110 days and there was never any dip in his dedication level throughout the course of the shoot. On most days, even after we packed up, he'd sit and discuss scenes for the next day," he said.Produced by Dil Raju, the film has music by Devi Sri Prasad and cinematography by Ayananka Bose.