Flying Head Xiaokai: Regular Chinese characters as big as a fly’s head, referring to extremely small regular script. Also known as "Fly-head regular script". King Zhong: Zhong Yao, a famous calligrapher and politician from Cao Wei during the Three Kingdoms period, and Wang Xizhi, a famous calligrapher from the Eastern Jin Dynasty.
It means that if you use characters the size of a fly's head and the size of a black silk, you can become a teacher if you write like Zhong Yao and Wang Xizhi