Before scaling a product, you need **six reference customers** — real users from the target market who are actively using the product, paying for it (if applicable), and willing to tell others about it. Not beta testers who tried it once. Not friends doing you a favor. Not people who said "I would buy that" in a survey. Actual users with actual results who will put their reputation on the line to recommend you. If you cannot find six, you have not achieved product/market fit. Cagan positions this as the critical gate between discovery and scaling — the point at which you have earned the right to invest in marketing, sales, and growth.