郑人买履
zhèng rén mǎi lǚ
lit. the person from Zheng 鄭|郑[Zheng4] who wanted to buy shoes (an allusion to an ancient story about somebody who, when buying a pair of shoes, preferred to rely on their foot measurements rather than just trying them on) (idiom)
fig. disregarding the sensible approach in favor of adherence to a fixed idea
Zheng man (郑人) + buy (买) + shoes (履) = trusting rules over reality
The story tells of a man who forgot his measurements at home and refused to simply try the shoes on his own feet. It became a byword for rigid, abstract thinking that ignores the plain evidence right in front of you.
他不肯试试新方法，真是郑人买履。
tā bù kěn shì shi xīn fāng fǎ, zhēn shì zhèng rén mǎi lǚ。
he refuses to try new methods — he is truly like the person from Zheng who wanted to buy shoes.
做事要灵活，不能郑人买履，死守老规矩。
zuò shì yào líng huó, bù néng zhèng rén mǎi lǚ, sǐ shǒu lǎo guī ju。
one must be flexible in doing things and cannot be like the person from Zheng who wanted to buy shoes, rigidly clinging to old rules.