Rajkumar Hirani is one manipulative director. The man doesn't just know his job. He in fact brings in a different dimension to his job, hence following the very philosophy that he advocates in the film. In one of the crucial scenes simply told, one of the three protagonists challenges the entire point behind studying - 'Is it merely about following what is already in place? Or is it about inventing something out of all that has been established?' Raju does something similar while telling a story through his movie. He learns from some great cinema that could have been made in different parts of the world and comes up with something as original as 3 IDIOTS which doesn't have any predecessor and tells an absolute fresh story.
Rajkumar Hirani follows the basic principle of story telling - 'Don't bore your audiences'. He doesn't and while doing so, he manipulates the entire story telling in such a manner that you just go with the flow. He makes you laugh hysterically, he brings on the smiles and in the process of doing so he makes sure that you also weep incessantly. The tears belong to the kind which flow not because you are laughing non-stop (as it happens in a Priyadarshan film) or getting emotionally charged (as witnessed in a couple of Sanjay Leela Bhansali films). They flow because Raju creates such scenes where a viewer shifts gears from being attentive to sheer euphoric. The idiom of 'smile on your face with tears in your eyes' fits in perfectly well in the story telling of Rajkumar Hirani and hence the reason why he gets hailed as one 'manipulative director' - of course in a positive sense!