expression
the frog in the well knows nothing of the great ocean
Proverb meaning that a person with a narrow perspective cannot understand the wider world. Often used to caution against arrogance born of limited experience.
井の中の蛙、大海を知らずというように、自分の経験だけで判断してはいけない。
As the saying goes, 'the frog in the well knows nothing of the great ocean,' so you shouldn't judge based only on your own experience.
A shorter form of the same proverb, often used as a set phrase meaning 'a person of narrow outlook.'
From a classical Chinese parable in the Zhuangzi, where a frog living in a well boasts of its world until it hears about the vastness of the ocean.