Often times even the geniuses in Silicon Valley don't know how great of a product they have until it is beyond popular.
During the early days of Facebook, for example, the founders were busy working on side projects, even as users were breaking down the front door asking to be let onto the platform. The first version of Instagram was a massive failure. The list is long.
Once the product is popular though, the geniuses can do a lot of things wrong and still succeed because the core of their success is so strong, it cannot fail.