Deciding which market to enter next is often based on broad analyst reports or internal intuition, both of which lack the granularity of real-world buyer behavior. The most expensive mistake a company can make is entering a market where they have no path to a competitive advantage. Win/loss analysis allows growth leaders to "stress test" a market before committing significant capital, providing a clear-eyed assessment of whether the current product and team can actually win. This keynote explores how to use win/loss data as a rigorous qualification tool for market expansion. We will discuss how to move beyond market size and look at market "winability," using feedback from early pilots and adjacent-segment deals to decide whether to double down or walk away. Key learnings will include: - Developing a scoring rubric to assess new market viability based on historical adjacent wins and losses. - Identifying hidden barriers to entry, such as entrenched incumbents or technical requirements, through lost-deal post-mortems. - Aligning executive leadership on a go/no-go decision framework backed by objective buyer evidence rather than optimism.