Julia Barham's stage model for a product's life: 0 to 1 (finding it), 1 to n (growing it), and at scale (running it) — each stage has different goals, activities, and metrics, so the right process for one stage is often the wrong process for another.
Notably, even a product that has reached scale can meet the criteria for sunsetting; maturity is not a one-way ratchet toward permanence.
Related: S-Curve Evaluation (Next Growth Wave vs. Enhancer), Four Types of Post-PMF Product Work (Reforge Framework), Product Stage as the Primary Fit Factor for Product Leadership.
Julia Barham extends the lifecycle model by adding explicit criteria and red flags for deciding when a mature, 'at scale' product should be sunset rather than kept running. The lifecycle stage isn't just descriptive labeling — knowing a product is mature is what licenses an active decision to retire it once those red flags appear, rather than letting it quietly absorb capacity from the Four Slices of the Pie (Product Portfolio Balance) by default.