A Very Important Question

Rating: 1/10 (9 November 2014)

I just have 1 question. In the movie, towards the end, Shah Rukh Khan and Boman Irani enter the Safe(or locker) where the diamonds are kept. The locker gets locked and they exit through the top. My question is why can't they enter through the top considering the fact that they already had the plans for the entire building?
I do not think that the writers envisaged the situation. It would have been pretty simple and slick. This goes on to show that enough thought was not put into the script.
A movie of this budget and the involving the slew of big names cannot overlook such a simple fact.
However, if anybody has any plausible explanation, please reach me at nishith4online@gmail.com.