expression
person ignorant of the wider world; frog in a well
Proverb describing someone with a narrow perspective who is unaware of the larger world. Often used critically or self-deprecatingly. The literal image is a frog that knows only its well.
彼は井の中の蛙で、海外の事情をまったく知らない。
He's a frog in a well and knows nothing about the situation overseas.
井の中
There's a saying: 'The frog in the well knows nothing of the great ocean.'