Today’s Chengyu, 井底之蛙 （jing3di3zhi1wa1), refers to a parable from the works of the fourth-century BC Daoist philosopher Zhuangzi (庄子). In this tale, a frog is sitting happily in a small pond at the bottom of a well. A sea turtle is passing the well and looks down into it. The frog calls up to the turtle to come and join him, as he is completely happy in the best of all possible homes. The turtle suggest instead that the frog come up and join him in returning to the ocean, which is far bigger and finer than the frog’s pond. The frog cannot understand how this is possible, and decides to remain where he is.
The literal meaning of the 成语 is “frog at the bottom of the well” and is used to describe someone narrow-minded and not open to new ideas. It’s used as a subject or object, or as an attributive. It is derogatory in nature and is often used to criticize or admonish.
More on usage: One can say 你是井底之蛙 to point out this flaw of narrow-mindedness in
another; one can also say 别做井底之蛙 to say “don’t be a narrow-minded person.”