A set of signals Barham lays out in her book to help a PM judge, informally, whether they actually have product-market fit — as distinct from needing to pivot or keep iterating. It sits alongside more structured tools like the Product Market Fit Pyramid as a faster first pass: run the sniff test before investing pyramid-level analysis, and definitely before treating a product as ready to receive growth investment. Paired in practice with the Chasing Growth Before Product-Market Fit (Leaky Bucket) pre-growth checklist (retention + ICP).