Year 2014 was very special to Korean mathematical society. Year 2014 was the Mathematical Year of Korea, and the International Congress of Mathematicians "ICM 2014" was held in Seoul, Korea. The year 2014 was also the 330th anniversary year of the birth of Joseon mathematician Hong JeongHa. He is one of the best, in fact the best, of Joseon mathematicians. So it is worth celebrating his birth. Joseon dynasty adopted a caste system, according to which Hong JeongHa was not in the higher class, but in the lower class of the Joseon society. In fact, he was a mathematician, a middle class member, called Jungin, of the society. We think over how Hong JeongHa was able to write his mathematical book GuIlJib in Joseon dynasty.