囊萤映雪 — “To study diligently despite difficult circumstances”

In the Jin Dynasty, Che Yin was studious from a young age. As his family was poor and couldn't afford lamp oil for him to read at night, he ingeniously caught fireflies on summer evenings, put them into a white gauze bag, and hung it above his books, using their faint light to study.

In the same era, Sun Kang, also from an impoverished family, would read by the reflected light of snow that illuminated his window on snowy nights.

This idiom thus symbolizes diligent study under challenging conditions.