Product-market fit is the most used and least understood phrase in startups. It is not a metric you hit or a box you check. It is the unmistakable moment when a market stops needing to be convinced and starts pulling the product out of your hands.
Before fit, everything is a push: sales are a grind, users trickle in and drift away, growth requires constant effort. After fit, the dynamic inverts. Customers find you faster than you can serve them, usage sticks, word spreads on its own, and the problem shifts from finding demand to keeping up with it. Founders who have felt it describe it as obvious in hindsight and hard to fake.
People look for a single number, retention above some threshold, a survey score, a growth rate, and those signals help, but fit is really a pattern across all of them: strong retention, organic pull, and customers who would be genuinely upset to lose the product. No one number captures it, which is why it is described as felt more than measured.
The most expensive startup mistake is pouring money into growth before fit exists, which just buys users who leave, scaling a leak. In regulated markets the temptation is worse, because the cost of building is high and the pressure to show traction is real. Fit first, then scale. This is general information, not investment advice.
When the market pulls, you will know.