Product-market fit

Before it, every sale is a fight. After it, customers arrive faster than you can serve them and the bottleneck moves to delivery. Most founders know the difference immediately.

It cannot be reached by better marketing. Marketing amplifies a signal; if the signal is not there, more spend just produces more expensive silence.

There is a measurable version, which beats the feeling. What share of users would be very disappointed if the product vanished tomorrow, and what share of last month's cohort is still using it this month? A retention curve that flattens, at any level, means a group of people for whom this is now part of their week. A curve that decays to zero means the product was interesting once.

It is also not permanent. Fit exists between a product and a market at a moment, and competitors, platforms and prices all move. Businesses that had it and lost it usually failed to notice for a year, because revenue lags retention: the customers who will leave have already stopped using it while they are still paying.