井底之蛙 (jǐng dǐ zhī wā)
Once upon a time, a sea turtle came upon a frog that lived in an old abandoned well. Upon seeing the turtle, the frog boasted: “Look, I am happy and completely at ease here. Why don’t you come down and join me?” The turtle tried, but the well was too small, so the turtle didn’t fit through the opening. Then, he said to the frog: “Have you ever seen the ocean? It is quite vast, and you would truly be happy if you lived there.” Upon hearing this, the frog was so surprised he just stood there speechless. Nowadays, this idiom is usually used to describe people who are not only short-sighted, but also complacent.