The Price Tag Lies
When you look at a single number — the rent, the tax bill, the recycling rate — you are almost certainly looking at the wrong number.
A woman in Modena pays €550 per month for an apartment on the periphery. Affordable, compared to the centre. But she also pays €175 for the car she needs because there is no bus, €80 for fuel, and the equivalent of €50 in time she spends commuting. Her real housing cost is €855 — 51.5% of her gross income. The rent was the single number. The system cost was invisible.
This is a pattern. It operates everywhere single metrics are used to evaluate complex systems.
Modena's recycling rate is 78.9%, according to ISPRA's 2025 report. An excellent number. Treviso, designated European Green Capital 2025, reaches 87.2%. But the recycling rate measures what goes into the sorting stream, not what comes out. The plastic capture rate shows 58%, but the true material recovery rate for plastics is approximately 23%, once sorting losses and non-recyclable fractions are accounted for. Waste composition analyses consistently show that 70–85% of what people put in the general waste bin is recoverable material that never reaches the recycling stream at all.
The waste tax — TARI — is approximately €310 per household per year. It does not change based on how much waste you produce. The person who carefully separates everything pays the same as the person who throws everything in the general bin. The single number — the tax — hides the incentive structure entirely.
Consider energy. More than 50% of Italian residential buildings are classified in energy performance classes F or G, according to ENEA. In Modena, 72% of residential buildings were constructed before 1976 — the year Italy introduced its first energy performance standard. A pre-1976 apartment costs roughly €180 per month to heat. Retrofitted, it costs €60. The rent is the single number. The energy bill is the hidden cost that makes the cheap apartment expensive.
The Single Number pattern works the same way with people. In Italy, two out of three non-EU workers are employed below their qualification level — a 66.5% overqualification rate, the highest gap in Europe according to Eurostat. The job title is the single number. The credential recognition system — four institutions, two to three years, €2,000–3,000 — is the hidden structure that produces it.
DMAIC insists on measuring the whole system, not the convenient metric. The third discipline of structured thinking: always ask what the number is hiding.
