If you build it, they will come(?)

Shouldn’t you do market research first? What happens if you build it and they DON’T come? I always wondered about the concept of supply and demand. I mean really, shouldn’t it be Demand than supply? Why build it unless you have a reasonable expectation that someone’s going to want what you are going to supply? Yes, you can be first to the marketplace, however, I would rather be IN the marketplace, once I know there IS a marketplace.