After Emperor Gaozu Liu Bang's death, Emperor Hui took the throne, but his mother Empress Dowager Lü held real power. When Emperor Hui died, she ruled in his stead, appointing many Lü clan members as princes and marquises, making the Lü family all-powerful. As she lay dying, Empress Dowager Lü summoned her nephews Lü Chan, Prince of Lü, and Lü Lu, Prince of Zhao, appointing them supreme generals to command the Southern and Northern Armies guarding the capital Chang'an. She warned them, "When Liu Bang was emperor, he told his ministers, 'Anyone not of the Liu family who dares to call himself king must be attacked.' After I die, you must hold firm to military power. Do not leave your camp even for a step to attend my funeral!"
After Empress Dowager Lü's death, the Lü clan plotted a coup to seize the throne, but feared opposition from Liu Bang's old ministers, Grand Commandant Zhou Bo and Marquis of Jiangguan, Guan Ying, so they dared not act rashly. Zhou Bo and other ministers knew the Lü clan would eventually rebel and discussed eliminating them. Remembering that Li Ji, son of Marquis of Qucheng Li Shang, was a close friend of Lü Chan, commander of the Northern Army, they kidnapped Li Shang and forced him to order Li Ji to trick Lü Chan out of the camp. Li Ji had no choice but to go to Lü Chan and say, "The new emperor is still young. The nobles and commoners already know you are the King of Zhao. If you stay as general of the Northern Army instead of going to your fief, everyone will suspect you have ulterior motives, and disaster will befall you. Better to hand the Northern Army over to the Grand Commandant and go rule Zhao." Lü Chan, believing Li Ji was looking out for him, surrendered the seal of the Northern Army and went hunting with Li Ji. Zhou Bo then seized the Northern Army and wiped out the Lü clan. The world said Li Ji had betrayed his friend.
Later, the idiom "Li Ji Betrays His Friend" came to refer to someone who is disloyal and betrays their friends.
Source: *Book of Han*, "Biography of Li Shang"
Meaning of the Idiom: Later, the Chinese idiom "郦寄卖友" came to describe how someone is disloyal and betrays their friends.