to be confined within a circle drawn on the ground as a simple form of prison in ancient times

传说在虞舜时代，官吏画地为牢，犯罪的人也守法不敢走出。

idiom · to restrict oneself to a narrow range of activities or fixed rules; to limit one's own scope

做科研不能画地为牢，要多接触其他领域的知识。