Ye, pronounced shè in ancient times, was a city of the Chu State during the Spring and Autumn period, located about 30 li south of present-day Ye County in Henan Province. It was the fief of Shen Zhuliang. Shen Zhuliang, styled Zigao, called himself "Lord of Ye" and was a somewhat renowned "worthy man."
When Confucius traveled through the various states and arrived at Ye City, his disciple Zilu accompanied him. The Duke of Ye welcomed them warmly but, not knowing Confucius well, asked Zilu about his master's character. Zilu, caught off guard, hesitated and said nothing. Later, Confucius learned of this and told Zilu, "Why didn't you say this: 'He is a man who, in his zeal for learning, forgets to eat; in his joy, forgets his worries, and is so absorbed that he does not even notice old age approaching'—that is all."
In ancient times, "fafen" meant studying diligently. The idiom "fafen wang shi" means to be so focused and hardworking that one forgets to eat.
Source: *The Analects*, Chapter "Shu Er"
Meaning of the Idiom: Later, the Chinese idiom "发愤忘食" came to describe how one is so focused and hardworking that one forgets to eat.