My co-founder and I have been working in 2-week sprints to try and build a product that people will want. First, we built an app to set an agenda for meetings, then we built an OKR tracker. We had no real sense of who we were building these products for. Finally, we settled on a group of people we wanted to serve (freelancers, because I am a freelancer) and decided on an expensive problem we want to solve (helping then find interesting, well-paid, reliable work).
We built out a landing page to validate our initial concept https://clienttree.io/ and managed to get just over 50 sign-ups to the waiting list in the first two weeks. This was enough indication of interest for us to start building the MVP.