Fable
The bridge crew’s two notebooks
Villages on both sides of the river hired a bridge crew to build a bridge. Before starting, the crew did two surveys. The first recorded the real reasons people crossed the river: going to market, taking children to school, hauling grain to the mill, going to the clinic on the opposite bank during rainstorms. Each reason noted the time, frequency, and how people currently made do. The second recorded the age, income, means of transport, and literacy rate of the people crossing.
When the team lead handed the two sets of notes to the design group, he casually said, "They're all user needs, look at them together." So the design group drew a scenic bridge with an elevator, because the second set of notes said there were many young people, they liked taking photos, and they were willing to pay for aesthetics. The bridge was built beautifully and became a popular spot that needed improvement.
A month after the bridge opened, the village filed a joint complaint. The landscape bridge's steps were too steep—elderly people carrying grain simply couldn't get up them. An elevator was installed, but it only ran during peak tourist season and was locked in the off-season to save power. The flatbed carts for hauling grain were wider than the gap between the steps, so every crossing required splitting the grain into small bundles and making three trips back and forth. The scene written in the first note—'taking children to school on a stormy day'—had never been considered on the landscape bridge.
The work crew went back through their notes and only then discovered the problem. In the first set of notes, the task "transporting grain" had five sub-conditions: load-bearing, uphill, different surfaces in sunny and rainy weather, a fixed time window, and the need for two people to coordinate. In the second set of notes, "young people like taking photos" was a description of part of the people, but it was almost irrelevant to the task of "transporting grain"—young people did not transport grain, and the people transporting grain did not care about taking photos.
When they rebuilt the bridge the second time, the crew set new rules: first list tasks according to JTBD, writing clearly for each task the scenario, constraints, and success criteria; then treat user personas as additional conditions for each task, such as "the primary executor of this task is a woman over fifty, carrying an average load of forty jin." Tasks select the architecture; personas adjust the parameters.
The new bridge used a gentle slope design, with anti-slip paving and a rest platform in the middle. It was less pretty, but grain carriers could push their carts across in fifteen minutes. Fewer young people came to take photos, but the flow of market-goers across the river increased sixfold. The work crew later wrote this rule into their quotes: charge by the number of tasks, and let the portrait affect only the coefficient on the unit price.
Later, someone asked why they did not add a freight passage to the first bridge. The crew's answer was direct: once the main structure of a bridge is set, adding more is just applying a patch. If the task and the profile are mixed up at the blueprint stage, what gets built is a bridge that looks good on the surface but never solved the river-crossing problem.