 Born of the Cheongsong Shim clan (靑松 沈氏), during the late Goryeo Dynasty, he passed the examinations and entered the government at age eleven.At that time, general Yi Seong-gye had full control of the government and had eliminated most of his rivals throughout Goryeo.Shim On, fully realizing that the Goryeo dynasty was at its end, joined Yi's faction and worked hard in bringing about a new dynasty.