William is a foil for Margot and thus represents everything Margot is not: he is brash, loud, mean, cynical, and cruel. William is a consistently negative force throughout the story, and one of his primary motivations is to sow cynicism and dash hope. One way he does this is by denying that Margot wrote her poem on her own. William’s disavowal breeds doubt and adversity among the rest of the children and further ostracizes Margot. His cruel bullying is designed to deny Margot of her most valuable attribute: her imagination. To William, imagination is a dangerous thing. His actions ultimately reveal a deeper motivation of self-protection from hurt and disappointment. William perceives that imagination breeds hope of a better world, and hopes can be dashed or unfulfilled. In repressing Margot’s imagination and destroying her hopes, William lowers the children’s collective expectations and also protects himself from disenchantment.

If lack of sunlight causes Margot to shrink and wilt, it causes William to harden and act out, and he harms others in the process. William is unhappy and feels something is wrong, but he is ill-equipped to pinpoint or deal with the distinct source of his suffering. Margot’s love for the sun shines light on William’s deficiency of joy. Thus, William masks his confusion and unhappiness with a tough and unfeeling armor. Beneath it, he despises Margot’s weakness and resents her for her vivid imagination and real memories of the sun. This resentment fuels William’s intent to destroy Margot as he leads the charge to lock her in the closet.