A question that's been on my mind. Since this deck discusses B2C startups, how to do you reach out to a consumer on a telephone to determine if they would be a

A question that's been on my mind. Since this deck discusses B2C startups, how to do you reach out to a consumer on a telephone to determine if they would be a good customer? How do you figure out what that consumer wants? I see all the advice to do all of this stuff before writing code, but I see others that suggest "failing fast" by building something and seeing who ultimately uses it and what they use it for. Let's say I wanted to make a picture hosting site (I don't), I would find my unique selling proposition and build a site around that, get the URL out in front of people that probably want to host pictures, then see how many of them sign up and how many ultimately use the USP feature that I built. In my case it's not as broad or generic a concept, so I can't throw a URL out there and just see how many people sign up for the site. I mean I can but I can't expect that to actually work, for anybody to actually show up. I know there are online communities out there I need to reach, blogs that focus on the target audience I am reaching for, and quite possibly thought leaders. What am I missing when it comes to building and marketing a B2C product?