"You've found Product-Market Fit." It's one of the most exciting things a founder can hear—and one of the easiest things to misjudge. Many startups see a surge in user sign-ups, rapid revenue growth, or increasing investor interest and assume they've reached Product-Market Fit (PMF). They start hiring, raising capital, and scaling their marketing efforts. But here's the real question: Is your growth driven by genuine customer demand—or simply by short-term momentum?