The frog at the bottom of the well
Refers to a person with limited outlook, wisdom, or life experience; a narrow-minded person
Negative
人要放开视野，不能做井底之蛙 | Rén yào fàng kāi shìyě, bùnéng zuò jǐngdǐzhīwā
People must broaden their minds. They cannot be like frogs at the bottom of a well
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他真像只井底之蛙，不仅见识少，还嘲笑别人 | Tā zhēn xiàng zhǐ jǐngdǐzhīwā, bùjǐn jiànshì shǎo, hái cháoxiào biérén
He really appears to be narrow-minded. Not only does he lack any kind of life experience, but he also mocks other people
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Shoutout to 郭老师 for teaching me this one!
商汤 (Shāng Tāng) was the founder of the Shang Dynasty (1600 - 1046 BC); 大禹 (Dà Yǔ) was a mythical leader who tamed floodwaters (this is a story in it and of itself, and I won't cover it here.)
《庄子》(Zhuāng Zǐ), a work written by 庄子 (Zhuāng Zǐ, the same as in the title) during the Warring States Period (475 - 221 BC)
There was a frog who resided in a dried-out well. He loved his home, and he would boast about it whenever he got the chance.
One day, he heard a noise outside his well and hopped up to take a look. He saw a sea turtle nearby, and he immediately bellowed for the turtle to come see him. When the turtle obliged, the frog immediately began to sing praises about his wonderful home and how it suited his every need.
The frog's passionate words struck the turtle to the core, and he slowly inched forward so that he could take a look at the well's depths. When he reached the rim and peered down, however, he saw a pool of foul-smelling, algae-infested muddy water. On top of that, he also got his two front legs stuck on some of the rim's bricks. With no incentive or ability to continue onwards, he furrowed his turtle brow and began to retreat.
The frog, utterly oblivious to the turtle's reaction, continued to boast, but unexpectedly, the turtle cut him off by asking whether the frog had ever seen the sea. The frog hadn't, so the turtle explained that his own home was indescribably vast and deep, and was said to have been so since the times of great Chinese figures like 大禹 (Dà Yǔ) and 商汤 (Shāng Tāng).
Upon hearing this, the frog widened his eyes and was completely dumbfounded at the evidence of his own ignorance.