Farhan Alienated Himself for Karthik...

In order to be a good actor, one has to get the closest he can to adopting the character he intends to portray, which is exactly what Farhan Akhtar to become Karthik.

His character was scripted as a lonely introvert, far from socializing, and to bring this out in the best way possible, Farhan stopped meeting his friends, answering the phone, and even exercising. The only thing he couldn't keep away from was his family, and that is partly also because his children are too young to understand that his job requires him going away.

The self imposed seclusion was such an impact in fact, that Farhan ended up feeling quite depressed, a realistic experience in terms of gaining the substance of his character. The most challenging part, revolved around playing both Karthiks in such a way that they seemed like two parts of the same person - a split personality of sort.
Inevitably, it reminds one of a similar solitude the famous Hollywood actor, late Heath Ledger had taken to in order to essay his world wide acclaimed character of Joker in The Dark Knight, and his consequent rather controversial death.
As long as Farhan knows where to stop the act and retain his normalcy, the idealism to gain perfection is all good with us!