A man from the state of Zheng wanted to buy a pair of shoes. He measured his foot and placed the measurement on a chair. When he left for the market, he forgot to bring it with him. Only after finding a pair he liked did he remember.
"I forgot the measurement," he said.
He returned home to fetch it, but by the time he came back, the market had closed, and he failed to get the shoes.
"Why didn't you just try the shoes on with your own feet?" someone asked him.
"I would rather trust the measurement than trust myself," he replied.