This story is shared by China, Japan and Korea.  It is a story about a frog and a sea turtle.

There was a frog that lived in a shallow well. ” Look how well off I am here ! ” he told a big turtle from the Eastern Ocean. ” I can hop along the coping of the well when I go out, and rest by a crevice in the bricks on my return. I can wallow to my heart’s content with only my head above water, or stroll ankle deep through soft mud. No crabs or tadpoles can compare with me. I am master of the water and lord of this shallow well, What more can  a fellow ask ? Why don’t you come here more often to have a good time ? “

The turtle from the Eastern Ocean could get his left foot into the well, however, he caught his right calw on something. So he halted and stepped back then began to describe the ocean to the frog. ” It’s more than a thousand miles across and more than ten thousand feet deep. In ancient times there were floods nine years out of ten yet the water in the ocean never increased.

And later there were droughts seven years out of eight yet the water in the ocean never grew less. It has remained quite constant throughtout the ages. That is why I like to live in the Eastern Ocean. Then the frog in the shallow well was silent and felt a little embarrassed. (Source: )

This expression is also used in Korean everyday speech. Here are some examples:

우물 안의 개구리는 되지 않도록 많은 경험을 하고 싶어요.

So I don’t become a frog in a well, I want to have many experiences.

우리 아들은 학교 공부밖에 몰라서 우물 안의 개구리가 될까 봐 걱정이에요.

Because our son doesn’t study hard in school I am worried he might become a frog in a well.

세계 각국 사람들을 만나 보니 내가 그동안 우물 안의 개구리처럼 산 것 같아요.

Since you met people from all over the world it seems that I was just living like a frog in a well during that time.