The Chinese idiom “the frog at the bottom of the well” [井底之蛙，jǐng dǐ zhī wā] tells the story of a small frog that lived deep underground in an old well. The frog was born in the cold and dark well; it has never been outside of the well. All the frog knew of the outside world was the faint light far above it, which it took to be the sun.
One day, a bird flew down into the well and came across the frog. The bird said to the frog, “Come up to the outside world where it is bright and warm.” Upon hearing this, the frog laughed at the bird, thinking that the well was in fact the entire world.
The moral of this story warns against discounting things that lay outside one’s own viewpoint. This idiom is used to describe a person who have a limited experience of the world.