This document discusses validating that a startup's solution fits the problem it aims to address. It emphasizes the importance of validating assumptions about customers and their problems early in the design process. Customer interviews and surveys are recommended to test the hypothesis that a solution solves a problem customers care about and are willing to pay for. If validation fails to confirm the problem-solution fit, the startup may need to iterate its solution or pivot to a new problem. The goal is to avoid building something nobody wants by continuously validating assumptions with customers.