郑人买履

zhèng rén mǎi lǚzhengrenmailu

1. (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)
2. (fig.) disregarding the sensible approach in favor of adherence to a fixed idea

Study it in Yanamino