出自《晋书·车胤传》，形容学习非常刻苦。
From the Book of Jin, Biography of Che Yin, describing extremely diligent studying.
车胤是晋朝人，自幼喜欢读书，但由于家中贫穷，没钱买灯油供他读书，所以天黑后他就无法继续读书了。他想每天晚上多读一些书，但没有灯又怎么读书呢？为此，他非常苦闷，一心想要改变这种状况。
Che Yin lived in the Jin Dynasty. From a young age he loved reading books, but his family was too poor to afford oil for lamps. So once night fell, he could no longer read. He desperately wanted to read more at night but had no light source. This caused him great vexation as he wracked his mind for a solution.
一个夏天的夜晚，车胤没事在外面散步，他发现空中有很多小亮点飞来飞去，仔细一看，才知道是萤火虫。他突然想到，要是把那些小亮点集中到一起不就有足够的光亮了吗？借着光亮不就可以读书了吗？想到这里，他非常兴奋，急忙跑回家做了一个纱囊，做好后，捉了很多萤火虫放在里面。萤火虫在纱囊里飞来飞去，不断闪烁着光芒，把纱囊照得非常明亮。于是，车胤就用纱囊照亮读书。
One summer evening while walking outside, Che Yin noticed tiny bright lights flitting about – they were fireflies. Suddenly, he thought, if he could gather those glowing lights together, wouldn’t that provide enough illumination to read by? Excited by this idea, he hurried home and made a silk satchel. He then caught many fireflies and placed them inside the satchel. As the fireflies flew around blinking, they filled the satchel with a bright glow. Using this makeshift lantern, Che Yin could read late into the night.
孙康也是晋朝人，家里也很贫穷，没钱买灯油点灯。他白天到地里干活，没有时间读书，只有晚上才能读书。他经常在雪天夜里，靠积雪反射出来的亮光读书学习。
Sun Kang, another impoverished Jin scholar unable to afford oil lamps, would work in the fields during the day. At night, he would study by the faint light reflected off the snow.
后人把车胤和孙康的故事称为“囊萤映雪”。
Later generations coined the term “nang ying ying xue” (fireflies in a satchel illuminating the snow) to refer to the extreme diligence of Che Yin and Sun Kang in pursuing their studies despite hardship.