"Breaking up with a friend by severing the mat" is a Chinese idiom that comes from a story in the Three Kingdoms Period. At that time, Guan Ning and Hua Xin of the Wei State were very good school friends, but they had totally different characters. Guan Ning was a diligent learner with little interest in wealth or fame; while Hua Xin admired high social status and power, unwilling to study.

One day, when the two were tilling crops in the field, a bar of gold was dug out. With great joy, Hua Xin tried to pocket it. Guan Ning was indifferent to the gold. Another day, when a high-ranking official was passing by in his luxuriously decorated carriage, Hua Xin instantly dropped his book and came out for a better view. And he praised the official and his carriage to the skies when he came back.

Guan Ning, who was engrossed in his book, felt more and more disgusted with Hua Xin. So he drew out a dagger and cut the mat they were sitting on in two, separating himself from Hua Xin. The severing of the mat indicated the end of friendship with Hua Xin. From then on, "breaking up with a friend by severing the mat" became an idiom referring to the end of friendship.