To work or concentrate persistently on something without letting up, often to the point of fatigue.
彼は試験に向けて毎日根詰めて勉強している。
He studies persistently every day for the exam.
仕事に根詰めすぎて体調を崩した。
He overworked himself and got sick.
小説の推敲に根詰めて、夜中まで直した。
I kept revising the novel late into the night.