This question was asked by a Interviewer to people of different occupations, and you will be amazed by knowing the answer, answered by them.
To Doctor: Well, I think I can buy it in 6–8 months of practice.
To MBA: I'll require 11–12 months of hardwork.
To Engineer: Well, It would take 2–3 years of very hard work
To Mr. Ratan Tata*: I think….about 5 years.
Everyone was aghast
at listening to Mr. Tata's answer. Suddenly there was pin drop silence in the hall.
In disbelief
Interviewer then asked
to Ratan Tata: Why so long Mr. Tata?
*Mr. Ratan Tata answered: Well, BMW is a big company
*
Learning from the story 
1. Think Big. Thinking big is an attitute which can be developed.
2. There is magic in thinking big. The moment you start thinking big, you start getting answers also to make it happen.
3. Only thing stands between thinking Big and its manifestation is your *Decision*. Thats it.
Questions to ask ourselves⁉
*If you have really made the decision build a Big business; Make another decision of learning how to do it