Fable
A ruler that judges timber must be able to say which grain made it shake its head
In Wooden Bridge Town there was an old master craftsman who could tell whether a piece of timber was fit for the bridge just by touching it. When his apprentice asked why, he would often say: the feel is wrong. On small bridges and paths, everyone trusted him, and bad timber really was rarely let through.
Later, the town bought a silver ruler that could judge timber. The silver ruler was extremely fast and could pick qualified materials from thousands of pieces of wood. The foreman was first satisfied with the red and green marks: green goes on the bridge, red is returned, and no one has to wait in line for the master craftsman.
Suppliers began to complain. Some red-tagged timber was genuinely strong, with only rain marks on the surface; some green-tagged timber looked beautiful but had hidden cracks inside. The foreman could only say the ruler judged it that way—and even as he said it, he felt the ground give way beneath him.
Once the silver ruler rejected a batch of good wood. The bridge schedule was delayed, the supplier filed a claim, and only then did the town open it up for review, discovering that the silver ruler overemphasized surface water stains while ignoring internal strength. The first remedy was to make the silver ruler spit out a few more pretty words, but those words still could not guide the next step.
The town required the silver ruler to give reasons a person could use: which traces it mainly looked at, which trials it referenced, how confident it was, and in what situations a master craftsman needed to review. The reasons did not need to explain every speck of sawdust, but they had to be enough for the foreman to decide whether to retest moisture, change suppliers, manually re-inspect, or adjust the acceptance threshold.
Later, the red mark was no longer a black-box verdict. Suppliers could appeal, foremen could investigate, and inspectors could see the judgment chain. The silver ruler also didn't require lengthy explanations every time—low-risk timber passed quickly, while critical bridge materials had to leave a clear basis.
Everyone understood that explainability does not rely on making mysterious words sound nice, but on letting affected people know why a judgment appeared, whether it can be challenged, and what to do next. A reason that cannot lead to action is just another layer of fog.
Later the town applied the silver ruler to a larger bridge. The foreman did not require it to tell every detail as a story, only that key judgments could be reviewed, appealed and used to guide corrections. People gradually accepted that a good reason need not be lengthy, but must let others bear the consequences.