Fable
The foot-measuring ruler arrived at another dock
There was a shoe shop in Lugang that initially made boots only for local fishermen. The shopkeeper had measured many feet and knew how high the instep was, how thick the sole should be, and how much margin to leave for the rainy season.
The shoe shop later received a large order from an out-of-town dock. The manager still worked from the old size chart, because past repairs had been few and the ledger proved the sizes reliable. After the first batch of boots was delivered, returns kept coming. Dock workers carried salt sacks year-round, so their feet were wider; they walked on stone paving, not mudflats; and they wore boots for longer periods.
The shopkeeper's naive fix was to enlarge all boots by one size. Returns decreased a little, but new problems appeared: some people got blisters, some tripped, and some found the soles too soft. The assistant then suggested looking only at the single most common return reason. But each dock had different problems, and moving a patch from one place to another created new errors instead.
The old shoemaker took people to the new pier to measure feet, observe roads, and ask about working hours, and compared these records side by side with the original Lukang data. For the first time, they saw that the two groups of customers did not come from the same world.
The shoe shop re-divided its size chart: fishermen, salt workers and ship repairers each had their own samples and acceptance rules. Orders from new places had to run a small trial batch first before deciding whether to continue using the old machines. Later, whenever the shoe shop arrived at a new dock, the first thing was no longer to start work as usual, but to confirm whether the people, roads, weather and usage patterns of this place still matched the old ledger.
The shopkeeper first blamed the craftsmen for being lazy, then had everyone sew the stitches more densely. The boots became sturdier, but still pinched, because the problem was not the craftsmanship but that the feet of the old town had been treated as the feet of every port.
He took a ruler and stayed out of town for seven days, measuring feet, observing roads, asking about working hours, and taking apart every returned boot one by one. The new size chart changed only a few inches, yet it overturned many assumptions.
The shoe shop later still kept the old ledger, but tried on every new dock first. Past good results can only explain the past; they will not guarantee the future in an unfamiliar place. The shopkeeper finally understood that a ruler being accurate in one place does not mean it is still accurate when the people and setting change.