Total Addressable Market is one of the most misunderstood concepts in B2B strategy. Too many founders inflate their TAM with generic industry reports, while others undersell their opportunity by thinking too narrowly. In this video, TK Kader demystifies market sizing with a practical, step-by-step approach that produces numbers you can actually defend in investor meetings and board presentations. He covers the three core methodologies --- top-down, bottom-up, and value-theory --- and explains when to use each. More importantly, he shows you how to derive your TAM from real customer data rather than analyst reports, making your market sizing both credible and actionable. Kader also addresses the common trap of conflating TAM with SAM and SOM, and explains how to present each layer of the market sizing pyramid clearly. This is essential viewing for founders preparing fundraising decks, product marketers building business cases, and GTM leaders sizing new market opportunities.