“Yíwènsānbùzhī” is used to describe someone knows nothing. e.g.
A: Lǎobǎn, nǐmendefúwùyuánzěnmeyíwènsānbùzhīa?
Hi,Boss!Your guys they know nothing.
I’m really sorry, they are freshman.
This story comes from “Zuozhuan”，B.C.468, jin attacked zheng ,and qi send an army to help zheng. The general’s name is chenzicheng. A private whose name is gouyan reported to chenzicheng, said that “A jin private told me that jin planted to send thousand privates to attack us, they want to wipe out all of us”. Chenzicheng called him said” Even if the enemy more than one thousand, we also have to fight with them, we cannot put ourselves down. And I will tell monarch what you just said. ”Gouyan realize that he made a mistake, clever people should consider the start , development, and result when they plan a thing. If you don’t know this three parts, you should never report to your superior.