A cohort retention curve that flattens over time — rather than continuing to decay — is the signal that a user base has stabilized enough to fund scalable growth. That stabilized value shows up in one of two forms: revenue (which can be reinvested into acquisition) or content/artifacts (which can be distributed virally).
Once a base is retained and monetizing, it can fund exactly four scalable growth channels:
The diagnostic move is to plot retention by cohort, watch for the flattening point, and then check which of these four channels the flattened base can actually fund or fuel — a marketplace or product without a flattening curve has no scalable growth model yet, regardless of which channels it's nominally running.
Measured using the Cohort Analysis Framework: Value-Action × Time. Distinct from PMF as Complaining Instead of Churning (Casey Winters), which is about defining PMF itself rather than what a stable retained base subsequently funds.