井底之蛙 (jǐng dǐ zhī wā): lit. a frog at the bottom of a well; fig. a person of limited outlook and experience

lit. a frog at the bottom of a well; fig. a person of limited outlook and experience

The frog who thinks the well is the whole sky. Same image as the Japanese 井の中の蛙, and used the same way: for someone judging a world they have not seen.

The same saying in Japanese: 井の中の蛙、大海を知らず

A Chinese idiom (成语)