Emperor Taizong therefore continued to siege Ansi. During Ansi's siege, part of Ansi's city walls collapsed, and Tang forces had an opportunity to enter, but at that time, Fu Fu'ai (), an officer under Li Daozong, was not paying attention, and instead Goguryeo forces fought out from the breach and captured the part of the offensive earthworks that Li Daozong was responsible for, using it instead for defense. For this offense, Emperor Taizong executed Fu, and when Li Daozong, baring his feet to show remorse, requested forgiveness, Emperor Taizong rebuked him but kept him in command of his forces.
In the context of the siege of Ansi, Emperor Taizong's decision to continue the assault led to a critical moment during the battle. During this time, a section of Ansi's walls collapsed, and Tang forces had an opportunity to enter, but at that moment, Fu Fu'ai was not paying attention, and instead Goguryeo forces fought out from the breach and captured the part of the offensive earthworks that Li Daozong was responsible for, using it instead for defense. As a result, Emperor Taizong executed Fu, and when Li Daozong showed remorse by baring his feet, requested forgiveness, Emperor Taizong rebuked him but kept him in command of his forces.