Why did Nawfal ibn Mu'awiyah advise the Prophet, peace and blessings be upon him, to lift the siege on Ta'if and depart from it?

The Prophet, peace and blessings be upon him, consulted Nawfal ibn Mu'awiyah al-Dili regarding the siege of Ta'if after fifteen days. Nawfal advised that Thaqif were like a fox in its den: if one persisted, they would be captured, but if left alone, they would not cause harm, indicating the futility of remaining. The Prophet, peace and blessings be upon him, agreed to this and withdrew because Thaqif were prepared for the siege, and the Companions had sustained injuries. Al-Bukhari and Muslim narrated that the Prophet, peace and blessings be upon him, said, "Indeed, we are returning, if Allah wills," after the Companions had been wounded.