Also in 429, at the advice of Cui, and against the advice of all other officials and his wet nurse Nurse Empress Dowager Dou, Emperor Taiwu attacked Rouran. (Cui believed that further major conflicts with Liu Song were inevitable, and that Northern Wei must first deal Rouran a major defeat to avoid being attacked on both sides.) However, Cui did not accompany Emperor Taiwu on this campaign, although he did inform Kou, who was, that the main Rouran force must be found and destroyed. When Emperor Taiwu engaged Rouran and dealt it a major loss, but was unable to find its Mouhanheshenggai Khan, Yujiulü Datan, he did not want to advance any further in fear of a trap, and even when Kou informed him what Cui had said, he stopped the pursuit. Only later did he find out that he was actually close to Yujiulü Datan's position and could have easily found and destroyed Yujiulü Datan, and he regretted this greatly.