A man from the state of Zheng was going to buy himself a pair of shoes. Before he left for the market, he measured his feet with a piece of string. He cut the string to match the size of his foot. Then he got dressed and set off for the market.
It was quite a long walk, and by the time he got to the shoe store, it was almost noon. He wasted no time. He picked out a pair which he liked very much, but before he could make up his mind, he wanted to measure them against the string to make sure the size was right. He turned every pocket inside out. The string was not there. He had forgotten to bring it!
"How forgetful I am!" he thought, "I'll have to go back to fetch it."
He put the shoes down on the counter and went home. He was right. He had left the string on the chair. He grabbed it and ran back to the market as fast as his legs could carry him. But alas, by the time he got there, the market was over and the shop was closed. He stared at his string, looking forlorn.
"If only brought the string the first time!" he said.
A passerby heard him and asked,
"You're buying shoes for yourself, aren't you? Why didn't you try them on?"
"Try them on my own feet?" the man from the state Zheng responded with surprise, "I'd rather trust the string!"
From that story comes the idiom 郑人买履. 郑人 means a man from the state of Zheng, 买 means " to buy", 履means "shoes" in formal Chinese. This idiom was used to mock those who believe only in dogmas and ignore reality.