The most fundamental difference between the movie and the book is that while the book talks about making the best out of the existing educational system in India, the movie tells us to rebel against the pressure inducing tactics of our Educational System and change it.
Hence, in the book, Alok's character, despite having Painting as his primary interest, still ends up being an Engineer, because it offers him a more stable career. But in the movie, Farhan quits Engineering, despite his family's pressure, and takes up Wildlife Photography as his career, because that is where his heart is.
Ryan's character in the book is that of a rebel, who is not able to channelize his brilliance in the best possible manner and hence despite his brains is not able to do well academically. Rancho on the other hand is an extremely intelligent and free-thinking boy who not only fights against the system but manages to trimuph over it in the end.
The book talked about how we end up losing our happiness when we try to pursue success very hard...and the movie showed that when you start pursuing excellence in anything you do, success will follow automatically.
The book and movie are actually pretty different from each other...specially, because some of the key sequences which made 3 Idiots so remarkable are completely absent from the book!
Nevertheless, it wouldn't have killed VVC and Company to put Chetan Bhagat's name in the beginning credit rolls of the movies! It would have only made them look like large-hearted people instead as the petty bunch of cry-babies that they have been made out to be in the last one week since the controversy came out!
Similarly, Chetan Bhagat could have just kept quiet and let those people enjoy their day of glory! Afterall, his book is already a cult classic in India...the movie cannot take away the fame that the author has already achieved! By giving contradictory statements, he has only come out looking like the fourth idiot in the entire row!
PS: Both parties have benefitted enormously though! The books sales of FPS are sky-rocketing in the last week and the movie is doing superbly well and is being talked about all over!
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