In the novel Fate Comes from Ma Xian, Guo Ziming was originally Ma Chao's confidant, and his martial arts was also very high. But for some personal reasons, he betrayed Ma Chao and became a traitor. The specific reason is not clear in the novel, but it can be inferred that it may involve personal interests, grievances and so on.

The above information is for reference only, and the specific reasons need to be understood by reading novels or watching TV dramas.