After Emperor Wen of Sui, Yang Jian, ascended the dragon throne, he appointed his eldest son Yang Yong as Crown Prince and enfeoffed his second son Yang Guang as the Prince of Jin. Unexpectedly, Empress Dugu disliked Yang Yong and frequently criticized him before the emperor. Being extremely henpecked, Emperor Wen gradually grew distant from Crown Prince Yang Yong.
Yang Guang, Prince of Jin, was born clever and handsome. By age ten, he loved poetry and books, dabbling in astronomy, geography, and the hundred schools of thought—but he was treacherous and scheming, obsessed with seizing his elder brother's position as crown prince. Yang Guang excelled at pleasing his father, Emperor Wen of Sui, and his mother, the empress, with perfect etiquette. Even when lowly servants or maids sent by them arrived, he would greet them at the gate, offer fine wine and delicacies, and send them off with generous gifts. Thus everyone praised Yang Guang as filial and benevolent. Using gold, silver, and jewels, he bribed Grand Preceptor Yang Su, instructing him to slander Crown Prince Yang Yong before the emperor.
Yang Su was the most meritorious official under Emperor Wen of the Sui Dynasty, and his advice was always followed.
One day, Emperor Wen sent Yang Su to Renshou Palace to observe Crown Prince Yang Yong's behavior. Upon returning, Yang Su reported, "The Crown Prince's demeanor is unsteady, with a look of resentment on his face. It seems his intentions have changed—Your Majesty must guard against any rebellious thoughts."
Thus, Empress Dugu sowed discord within the palace while Yang Su spread slander outside, deepening Emperor Wen of Sui's prejudice against Yang Yong day by day. Finally, in the twentieth year of the Kaihuang reign, the emperor deposed Crown Prince Yang Yong, reducing him to commoner status and imprisoning him in the Eastern Palace, appointing Prince Jin, Yang Guang, as the new crown prince. That very night, a fierce wind and heavy snow struck, earthquakes shook the mountains, many civilian homes were destroyed, and over a hundred commoners were crushed to death.
After Emperor Wen of Sui passed away, Yang Guang ascended the throne, becoming known in history as Emperor Yang of Sui.
Yang Su, believing he had rendered great service to Emperor Yang, swaggered in and out of the court, even addressing the emperor as "Young Master" (like a nobleman's son). His power and influence grew so immense that most civil and military officials feared and avoided him. Anyone who crossed him would be dismissed from office at the least or executed at worst; with half the court under his control, it was as if there were two emperors in one dynasty.
Later, the idiom "complacent and self-satisfied" came to describe a state of being very pleased with oneself.
Source: *Taiping Yulan*, Volume 106
Meaning of the Idiom: Later, the Chinese idiom "扬扬得意" came to describe a state of being very pleased with oneself.