Most folks think that building a product is the hard part..."if we can just build the [web site, widget or product] then we are going to be Golden!" Building it is the easy part. How will you connect the product with enough customers in a short enough time span to survive? That is the when the work starts.
To have a business you have to have a great product ("Everybody is going to LOVE this widget!") that addresses a pain point, that is different enough that the public will respond, and priced in a way that the public will buy.
All of these things have to be done for you to have a business, but these are the EASY parts.
Your business really starts when you have got all of these things done, and then you are ready to connect the product with an indifferent public. Consider having all of these things done as a "Ticket to the Game." The fact of the matter is that people don't care about your idea.
People are busy.
The challenge for the entrepreneur is to make the customer care- to effectively communicate the value proposition and drive people through the transition from not knowing anything about your product, to understanding about you and your product -- and gladly paying for it.
Building your product is necessary, but keep that accomplishment in perspective - building a car without a plan to get gasoline won't get you anywhere. Build your idea and focus on answering the critical question of how you connect that idea with the enough people in a short enough period of time that you not just survive, but thrive.