Your first customers require obsessive, daily interaction to ensure the product works for them. Astronomer's founder spoke with their first managed Airflow customer four times a day for two months. This grueling process is essential for ironing out roadblocks and achieving product-market fit.

Runway's founder knew he had found product-market fit not just from revenue, but when a major customer, AngelList, began running its business on the platform and became an evangelist. Deep adoption by a respected company is a far stronger signal of PMF than early sales traction alone.

Eve knew they had product-market fit when customers found a bug that let them bypass invite restrictions. Users onboarded their entire firms months ahead of schedule, demonstrating an urgent, unmet need for the product.

When a product addresses a significant need, early adopters will actively help you fix bugs and overcome hurdles. This intense engagement, despite product immaturity, is a powerful indicator of product-market fit. Users are willing to go "above and beyond" because the outcome is so valuable to them.

Product-market fit isn't just growth; it's an extreme market pull where customers buy your product despite its imperfections. The ultimate signal is when deals close quickly and repeatedly, with users happily ignoring missing features because the core value proposition is so urgent and compelling.

Initially, customers often "round down," focusing on missing features. A key sign of product-market fit is when they start "rounding up"—their faces light up in demos, and they imagine the product's future potential, forgiving current limitations because they believe in the core value.

The ultimate test of PMF isn't surveys or usage metrics, but how indispensable your product is. If customers don't immediately notice and complain when it's gone, you haven't achieved true dependency. It's a visceral, high-signal test for any founder.

In the early days, Canary's pitch received mixed reactions. However, the strong, visceral "I need this now" response from a few customers was a more valuable signal of product-market fit than getting a polite "that's cool" from everyone. This validates the "10 true fans" principle in B2B.

Airbyte's initial marketing product saw usage drop to zero when COVID hit and budgets were frozen. This revealed it wasn't solving a vital, mission-critical problem, forcing a necessary pivot towards a more fundamental infrastructure need.