Bill, unable to understand human love and relationships, accidentally says the exact thing Mabel needs to hear to remind her how much her brother does for her, how much she loves him and how important it is that she help him now. Sibling love triumphs over evil and a heartwarming conclusion is arrived at.
Bill may be alien enough that human emotions are hard for him to understand. But he ought to know a lot about human behavior. He’s older than our universe, has eyes everywhere and one of his main skills is manipulation and trickery. Why would he make such a seemingly obvious mistake?
For most of Sock Opera, Mabel is pretty focused on completing this play and impressing Gabe. Bill is completely confident that she’ll care more about the project that she’s been working obsessively on than the needs or desires of her brother.
I wonder who could have given him that impression? Made him confident that she’d place the object of her obsession above everything else? Made him believe she’d put it above the needs of her brother? Made him believe she’d abandon him?