The business didn't fail because it lost to a better competitor. It failed because the thing it was competing to provide stopped being something the world needed in the form it was providing it. The market didn't move to someone else. The market moved on. The business was left behind, still organised around a utility that was evaporating, serving a customer whose behaviour had already structurally changed.
DZ5 is the most common primary classification in the 198 — 49 companies, nearly a quarter of the dataset. That frequency is the point. Relevance is not a permanent condition. It is maintained actively or lost gradually. The horizon doesn't announce itself. It is crossed quietly, often while the business is still growing, often while every internal metric still points upward. By the time the crossing is visible in the numbers, the cost base, the identity, and the incentive structure have all been organised around a position that no longer exists.
The cruelty of DZ5 is that the businesses that land here were usually right — once. The category was real. The customer need was genuine. The model worked. What it couldn't do forever was remain the best answer to a need that the world found better answers to. The failure was not in building the wrong thing. It was in assuming the right thing would stay right without active, ongoing work to make it so.