"Yeyijiri" literally means night following day, describing doing something continuously without distinguishing between day and night. It originates from the phrase "The noble, night following day, contemplate goodness and evil" in Zhuangzi: Perfect Happiness. It originally referred to people of noble status thinking day and night about how to do good, and later came to broadly mean being diligent and hardworking, racing against time. Its deeper meaning emphasizes that when time is pressing or tasks are heavy, one must make full use of every moment. It is often used to praise the spirit of selfless work and diligent study. It is mostly used in contexts describing scientific research breakthroughs, emergency rescue and disaster relief, exam preparation sprints, and other situations requiring sustained commitment. Its emotional tone is generally positive, but it can also be used in neutral narration, implying excessive fatigue. In terms of cultural background, it reflects the traditional Chinese virtue of diligence and resilience. It is similar in meaning to "giving up sleep and forgetting food" and "all night until dawn," but places more emphasis on actively making use of nighttime hours.
📝 Example
In order to complete the new drug research and development project on schedule, the research team worked day and night and finally made a breakthrough. ("夜以继日" here means the team worked continuously around the clock, highlighting their diligence and sense of urgency.)
On the eve of the college entrance examination, he reviewed his lessons day and night, scarcely getting a full night's sleep. ("夜以继日" here means he studied without stopping day or night, describing his diligence and dedication in preparing for the exam.)