He has been part of the Hindi film industry for four decades now but Bollywood megastar Amitabh Bachchan says he refrains from "excessive commentary on films" as his knowledge of the medium is "beyond zero".

"I have prevented myself from excessive commentary on films after they are ready, primarily because my knowledge of the medium is beyond zero and secondly because each time I have, the film has crashed at the box office. So much for the 40 years of my so called association with the business, " Amitabh posted on his blog bigb.bigadda.com.

Big B, as he is fondly called, raised the topic while recalling a incident when he first saw his 1981 film "Laawaris" in Bangalore before it was sent to distributors and exhibitors for release.

Dejected at some of the "technical" glitches, the 66-year-old had then wanted to bring about changes in the Prakash Mehra movie.

"Disappointed at some of the final technical results of the film...lamenting the glitches and waiting for the morning to appear so I could speak to Prakash Mehra and express my anguish and hope that he would give in to my suggestions of the changes I had in mind.

"Apart from the fact that technically it was impossible to change anything...it was the calm and confident persuasion of my director that kept me from further despair. And more than that it was the massive success of the film that conveyed to me that I knew absolutely nothing and was completely out of sync with direction and the making of films, " Amitabh wrote on his blog.

Apart from Amitabh, "Laawaris" also starred Zeenat Aman, Amjad Khan and Raakhee.