Perhaps the best answer to this question lies in the realization that art is an imitation of life but can never be a substitute for it. As "she still delights/To weave the magic mirror's sights," the Lady of Shalott experiences the world and arguably lives her life vicariously through the images of the outside world that she glimpses in her mirror. Through the first two parts of the poem, she is content with this lifestyle as evidenced by her "song that echoes cheerly." However, upon viewing "two young lovers lately wed," the Lady utters "I am half-sick of shadows." In other words, her weaving of the images in her mirror, which arguably represent any artistic expression, cannot hold her or comfort her on a dark, lonely night. Thus, one can better understand her decision to follow the attractive Lancelot later in the poem.