"Soon after Ling Tong and Yue Jing were in a battle. While they were fighting Cao Xiu let fly an arrow that hit Ling Tong’s horse. As Yue Jing pounced forward another arrow was let go and hit Yue Jing right in the face. Ling Tong retreated back to his lines. “The arrow that saved you was shot by Gan Ning,” said Sun Quan. Ling Tong turned to his rival and bowed low. “I could not have supposed you would have rendered me such a service, Sir,” said he to Gan Ning. This episode ended the strife and enmity between the two leaders, who thereafter swore perpetual friendship."
www.kongming.net
Since Gan Ning killed Ling Cao, Ling Tong's father, and Ling Tong attempted to slay Ning for revenge more than once, why did you think Gan Ning shot that arrow right in Yue Jing's face saving Ling Tong?

