A radical promise sits at the heart of this book: start smaller than feels comfortable-and outgrow competitors who start big. If you've been told to chase a massive market, this offers a sharper alternative: master a tiny one so completely that expansion becomes a controlled consequence. You'll learn how niche marketing and a micro targeting strategy reveal the few levers that actually move growth, and why serving a real cohort of one hundred people can generate compounding advantages others miss. It's for founders, solo operators, product leads, and investors who value evidence over hype and want a playbook they can execute next week. You'll see how to achieve product-market fit in a micro-market, price the transformation you deliver, and tell a story the market believes. Expect field-ready tools: interview scripts for customer development, worksheets for unit economics, and a cadence that encodes customer obsession into daily work. - Find and serve your first one hundred true fans-then build a business with 100 customers that can scale - Turn a narrow problem into a category of one with real switching costs - Use bootstrapped growth maths to decide when to add capital or say no - Design gravity-referrals, data, and small network effects-for a small market big company If you're ready to trade vanity metrics for durable results, this is your map to the 100 customers rule-a focused path from quiet beginnings to meaningful scale.