Lets say you are a Byzantine General who is leading his theme,(Army) into battle against the Ottomans.
You make camp beside a canyon, you see the Ottoman camp on the opposite side. They send a courier to you, he tells you that you have no chance against his master, for he is a almost undefeated commander, and tells you to surrender. You must defeat the Ottomans here or they will go on to raid allied villages.
What do you do?