What is the reason for the Muslims fighting the Romans during the first three days of the Great Battle, despite their knowledge that victory will be on the fourth day?

The Great Battle (Al-Malhamah al-Kubra) between Muslims and Romans refers to a hadith narrated in Sahih Muslim, where they fight for three consecutive days, and each time a group of Muslim fighters is annihilated. On the fourth day, the remaining people of Islam launch an attack, and Allah grants them victory. If Muslims know the content of this hadith, then it is Allah's decree that cannot be averted. Whoever Allah has decreed martyrdom for among them will attain it, in fulfillment of His saying, the Almighty: "Say, 'Even if you had remained in your homes, those for whom fighting was ordained would have come out to their death beds.'"