Tang Jia Nan is a player, who likes to mess around but at the same time, he's a very nice person.
When he was little, his brother Tang Hao Yun lost one of his legs from saving him which caused Jia Nan to feel guilty ever since. To make it up to him, Jia Nan acts dumb which caused him to grow up to become a very simple person who has no interest in becoming his family's company, Bei Shi's, heir.
(Source: Wikipedia, xue er at mydramalist)