A new startup is a series of unresolved hypotheses. This article makes the point that the goal of a startup (explicitly via the Lean Startup, Minimum Viable Product route, or implicitly) is to test whether those hypotheses are true.
The goal of the Minimum Viable Product should be to test the founding vision or initial hypothesis. You need to be open to different answers - the answer might be a yes, a qualified yes, or a no. By framing the founding vision like a hypothesis, you remain open to multiple answers.
One approach I've found helpful to evaluate a new startup idea is to break the idea down into hypotheses, for example "there is demand for this type of product", "we can access that demand", "the product is technically feasible". Sort them by a combination of risk and uncertainty (often roughly in this order), and then work your way down the list, updating it as you go along.