Product-Market Fit
The point at which a product satisfies strong market demand, visible in retention rather than growth.
Product-market fit describes a product that a specific market genuinely wants. It shows up in behaviour: customers stay, use the product regularly, and tell others.
It is measured through retention, not acquisition. Growth can be bought; retention cannot. A cohort curve that flattens rather than decaying to zero is the clearest evidence.
Fit is not permanent. Markets shift, competitors arrive, and a product that fit two years ago may not now — which is why retention is monitored rather than declared.