郑人买履 (Zhèng Rén Mǎi Lǚ) — The Man from Zheng Buying Shoes
The Concept
English: Base Rate Fallacy — Ignoring general statistical information in favor of specific, individuating information; focusing on the particular while neglecting the general.
Chinese: 郑人买履 (Zhèng Rén Mǎi Lǚ) — The man from Zheng buying shoes.
Cultural Origin
This parable from the Han Feizi (韩非子):
A man from Zheng wanted to buy shoes. He measured his foot and placed the measurement on his chair. When he arrived at the market, he realized he had forgotten the measurement. He returned home to get it.
By the time he returned, the market had closed. He couldn’t buy shoes.
Someone asked: “Why didn’t you just try the shoes on with your feet?”
He replied: “I would rather trust the measurement than my own feet.”
The base rate fallacy is trusting the abstract measurement over the concrete reality; the map over the territory.
The Tyranny of the Measurement
The man had two sources of information:
- Base rate/general: The measurement (abstract, historical, potentially outdated)
- Specific/particular: His actual feet (concrete, present, directly relevant)
He chose the measurement. This is the base rate fallacy in reverse—usually we ignore base rates in favor of specifics, but here the man ignores the specific (his feet) for the abstract (the measurement).
Both errors stem from the same confusion: mistaking representations for reality.
Historical Manifestations
- The Imperial Exams: Officials selected based on examination results (measurements) rather than actual administrative ability (feet). The measurement became more important than the reality it represented.
- The Mandate of Heaven: Dynasties justified rule through celestial signs (measurements) even when their actual governance (feet) was failing.
- Confucian Ritual (礼): Ritual prescriptions originally designed to cultivate virtue became ends in themselves—the measurement worshipped while the feet of human flourishing were ignored.
Legalist Critique
Han Feizi, author of this parable, was deeply skeptical of traditional Confucian ritual. He saw in the man from Zheng a metaphor for those who clung to ancient texts and ceremonies while ignoring present realities.
The Legalist solution: look at your feet. Trust concrete results over abstract principles.
Modern Applications
The base rate fallacy appears when:
- Doctors ignore disease prevalence (base rate) in favor of test results
- Investors ignore market history in favor of hot stock tips
- Hiring managers ignore demographic qualifications in favor of interview impressions
- AI systems trained on biased data produce biased results
The man from Zheng would use an algorithm without checking if it works in practice.
The Lesson
The man from Zheng teaches that measurements exist to serve reality, not replace it. The wise person:
- Uses base rates as starting points, not conclusions
- Updates beliefs with specific evidence (Bayesian thinking)
- Never forgets that the map is not the territory
正如韩非子所言：“夫不适国事而谋先王，皆归取度者也。” (Those who plan for ancient kings rather than present circumstances are all like the man who went home for his measurement.)
Trust your feet. The measurement is a tool, not a master.