Enduring hardships and humiliation over a long period to achieve one’s goal (often used of patient endurance, revenge, or striving). A four-character idiom.
彼は臥薪嘗胆の覚悟で研究を続け、ついに成果を挙げた。
He continued his research with patient endurance and eventually achieved results.
臥薪嘗胆の精神で困難を乗り越えよう。
Let's overcome difficulties with the spirit of enduring hardships for a goal.