A frog in the shallow well -- A person with a very limited outlook

Have you not heard of the frog that lived in a shallow well? It said to a turtle that lived in the East Sea, "I am so happy! When I go out, I jump about on the railing beside the mouth of the well. When I come home, I rest in the holes on the broken wall of the well. If I jump into the water, it comes up to my armpits and holds up my cheeks. If I walk in the mud, it covers up my feet. I look around at the wriggly worms, crabs and tadpoles, and none of them can compare with me. Moreover, I alone occupy this well. I am lord of this trough of water and I stand up tall in this shallow well and enjoy all the joys of life here. Great happiness has fallen to my lot. I am perfectly happy! Why not often come in to visit my place, sir?"

The big turtle from the East Sea nodded assent and was going in to have a look. Before the turtle could get its left foot in the well, its right knee got stuck. It hesitated and retreated. The turtle told the frog about the East Sea.

"Even a distance of a thousand li (1 li = 500 meters) cannot give you an idea of the sea's width; even a height of a thousand ren (1 ren equal to 21/3 meters) cannot give you an idea of its depth. In the time of King Yu of the Xia Dynasty (21st century 　 12th century BC), there were floods nine years out of ten, but the waters in the sea did not increase. In the time of King Tang of the Shang Dynasty (17th century 　 11th century BC) there were droughts seven years out of eight, but the waters in the sea did not decrease. The sea does not change along with the passage of time and its level does not rise or fall according to the amount of rain that falls. The greatest happiness is to live in the East Sea."

After listening to these words, the frog of the shallow well was shocked into realization of his own insignificance and became very ill at ease. This set phrase metaphorically denotes those with a very limited outlook and experience. Moreover, the frog in a well can see the sky only as large as the mouth of a well and so it has merely a very narrow field of vision. Hence there is another similar set phrase  -- Looking at the sky from the bottom of a well.