Jack Cheng knew about protection. He knew who gave it and who needed it, and he knew that he was the one who'd found his sister curled around the toilet one night, sleepwalking into the swinging kitchen door another night, and that was a calling.
-- Jack (chapter 1)

Importance: The opening lines of the novel explain the role Jack feels he plays in his family—he sees himself as the protector of his little sister Annabel. In the early stages of the plot, this involves staying vigilant all night so he can ensure that Annabel does not hurt herself while sleepwalking, but Jack's protective sensibility later causes serious problems for the family when he claims he did not see what happened at the Thanksgiving party because he does not want to get his sister in trouble.

He was going to live with his parents, who seemed to him not people so much as a...
-- Jack (chapter 1)