In 87 BC, after Emperor Wu of Han died, his eight-year-old son Liu Fuling ascended the throne, known historically as Emperor Zhao of Han. Following the late emperor's edict, Grand Marshal General Huo Guang and Imperial Censor Sang Hongyang were appointed as regents, holding the military and political power of the court.
Huo Guang was fiercely loyal to the Han imperial family and implemented a series of measures that spurred significant economic growth during the Western Han Dynasty. However, he also wielded his power ruthlessly, executing political rivals like Sang Hongyang and even forcing dissenting nobles to commit suicide, cementing his fearsome reputation.
Emperor Zhao of Han died young at just 21, leaving no heir, so Huo Guang placed Liu He, Emperor Wu's grandson, on the throne. Soon discovering Liu He's debauched lifestyle of constant revelry, Huo Guang consulted with ministers and deposed him, instead installing Emperor Wu's great-grandson Liu Xun as Emperor Xuan of Han.
Liu Xun's grandfather, Liu Ju, was Emperor Wu's crown prince until he was implicated in a scandal that led to the execution of his entire family. Liu Xun, then just an infant, was spared only because a prison warden secretly rescued him and placed him in hiding with his maternal grandmother's family. Having grown up among commoners, Liu Xun understood firsthand the hardships of ordinary life.
However, Liu Xun was also well aware that Huo Guang wielded immense power, and his own life and position depended entirely on him, making him deeply fearful of Huo Guang.
After Emperor Liu Xun ascended the throne, one of his first major acts was to visit the imperial ancestral temple. On that day, Emperor Xuan rode in a lavishly decorated carriage, with Huo Guang seated beside him as his imperial advisor. Seeing Huo Guang's towering stature and stern expression, the emperor involuntarily felt a deep sense of fear and unease, as if sharp thorns were pricking his back—so unbearable was his discomfort.
After that, Emperor Xuan always acted cautiously whenever he saw Huo Guang. When Huo Guang died of illness in 68 BCE, the emperor finally felt unconstrained and free to move about, no longer having Huo Guang accompany him in the carriage.
"The idiom 'thorns in the back' means feeling as if small prickles from plants are stuck on one's back, describing a state of fear and restlessness."
Source: *Book of Han*, "Biography of Huo Guang"
Meaning of the Idiom: Later, the Chinese idiom "芒刺在背" came to describe feeling as if small prickles from plants are stuck on one's back, describing a state of fear and restlessness.