During the late Eastern Han Dynasty, Dong Yu, a lecturer to Emperor Xian, was a highly learned man, revered as 'Ru Zong' (Master of Confucianism). Many scholars wished to become his disciples and seek his guidance.

However, Dong Yu declined to take on students, asserting that books themselves were the finest teachers. He famously advocated, 'Read a book a hundred times, and its meaning will naturally reveal itself.'

When some scholars lamented their lack of time for study, Dong Yu advised them to make use of their 'three remnants of time': the idle days of winter, the quiet hours of night, and the dreary stretches of rainy weather, all ideal for reading and learning.