井底之蛙
jǐng dǐ zhī wā
Literal: The Frog (蛙, wā) at the bottom (底, dǐ) of the well (井, jǐng)
Actual: Someone who isn’t very knowledgeable, or with a limited worldview
There once was a Frog who was born in a well. It was ignorant of anything outside of the well - the sides were too tall and slippery to climb. Nevertheless, the Frog came to love the well as its only home, occasionally looking up to the night sky for entertainment. After all, there wasn’t much else to do without 4G coverage.
One day, the Frog heard a pitter patter above the well. A curious Sea Turtle looked down and asked: “You OK there?”
“Well of course!” The frog beamed, delighted with his guest. “I’m having an absolute ball. I can take all the baths I want, I rule over the tadpoles and the shrimp, and I have the full Star Trek collection on VCR. You should join me!”
The Sea Turtle was a bit skeptical at first - the well had a rather unpleasant stench, and the Sea Turtle was more of a Star Wars fan. “Oh well, I do like shrimp.” But as the Sea Turtle shuffled around, its large shell got stuck at the mouth of the well. After a few minutes of struggling, the Sea Turtle pulled out. It had a better idea.
“Why don’t you come and visit the ocean instead? That’s where I live. An infinite expanse water deeper than anything else. Even during the Great Floods, the ocean did not rise; during the Great Droughts, the ocean did not fall. And neither would happen, ever - well, barring a catastrophic change in atmospheric composition and global ecosystems. Obviously. Whaddya say? I’m on my way to the local book club - wanna join?” The poor frog simply sat there in disbelief, with its mouth open and its tiny mind blown.
TL;DR: Frog living in a well stunned by the concept of an ocean. Although the Frog eventually realized he couldn’t survive seawater, the duo built a pretty neat sandcastle instead.