“Apps that find solid secondary product market fit have almost triple the minutes with their daily active users and almost double the daily active user to monthly active user ratio... what Calm did really well is they were out to solve a set of user problems that have some common symptoms.”

Secondary Product-Market Fit Nearly Triples DAU Minutes and Doubles DAU/MAU Ratio

Google's internal data shows apps that find a secondary use case — Calm expanding from meditation to sleep stories — see engagement metrics nearly double and triple. The insight is to think about the underlying user problem (poor sleep, anxiety) rather than the feature category (meditation app). Secondary PMF comes from solving adjacent symptoms of the same problem, not from bolting on unrelated features.