expression
being ignorant of the ways of the world; knowing nothing of life
Idiomatic expression used to describe someone who is extremely sheltered or naive, lacking basic practical knowledge. The literal image is of a person who cannot even tell if a potato is boiled. Often used in a critical or mocking tone.
彼は芋の煮えたもご存じないようなお坊ちゃまだ。
He is a spoiled young man who doesn't know the first thing about the real world.
そんな芋の煮えたもご存じない人に、この仕事は任せられない。
I can't entrust this job to someone so utterly ignorant of how things work.
世間知らず is a more common and neutral term for someone ignorant of the world, while 芋の煮えたもご存じない is a stronger, more colorful idiomatic expression with a mocking nuance.
The expression literally means 'not even knowing whether a potato is boiled', implying a level of ignorance so profound that one cannot recognize something as basic as a cooked potato. The exact origin is uncertain, but it is a traditional Japanese idiom.