Final answer:
Thetis feared for Achilles' life due to a prophecy that he would live a short life if he chose the path of war, which led her to disguise him and hide his true identity to keep him away from battle.
Step-by-step explanation:
Why did Achilles's mother fear for his life? Achilles' mother, the goddess Thetis, was deeply concerned for her son's fate. According to prophecy, Achilles was destined to lead a short life if he were to embrace the path of warfare, which was considered almost inevitable due to the times he lived in. Aware of this doomed fortune, Thetis went to extraordinary lengths to conceal Achilles and avoid his participation in war. She initially hid him away under the care of the wise centaur Chiron, and later, to prevent him from joining the Trojan War, she disguised him as a woman among the daughters of Lycomedes, the king of Skyros. Despite these efforts, Achilles' desire for glory and his destiny proved too strong when Odysseus cleverly revealed his identity by placing weapons among an array of gifts—Achilles instinctively chose the arms, thus revealing his true nature.