In old China, to study hard and pass the imperial exam is the only way to be an official. This is not hard to understand I think. Officials in Ming Dynasty are divided into 1-9 levels, 1 is the highest and 9 is the lowest. The first emperor of Ming, Zhu Yuanzhang was a farmer and he knew how ugly the official were. He had very strict rule in administration. Spies could be found in any important official's family. Salary were low, compared with other dynasties. Any corruption would cause death. However, people always persume career as a govenment official. They study for being an official for health, grade and honor for whole family. I think the saying also refers to the exam system of Ming. Enrollment expansion was carried on and more people would have chance to be an official. So, it was popular.