It's hard to send a local book
It's hard to send a letter from home. The metaphor is isolated from the news of hometown. From Zhang Tai Ye Si.
The origin of Idioms
In zhangtai Yesi written by Wei Zhuang of Tang Dynasty, "you can't send the local books, but the autumn geese return to the south."
It's hard to send a local book
Clams become pearls from diseases - bàng bìng chéng zhū