Character Analysis
Don Armour (yeah, real subtle with the symbolism there, Franzen) shapes the future of the Lambert family, but he probably has no idea.
When we first meet Don in the Midpac Signals Department, it seems like he's just some slime-ball that won't impact the plot in a significant way. Don plays an important role in shaping the person Denise becomes, however—for better or worse—by providing the blueprint for the emotionally distant yet needy men that she'll come to be involved with.
Meanwhile, Alfred is telling us who Don really is. His hallucinations are haunted by "the blue-cheeked man from Signal" (4.953) who taunts him mercilessly. Remember the talking turd? That's Alfred imaginary manifestation of Don. Oh…
We don't fully grasp the situation until the very end of the novel. Denise's brief affair with Don—something that she didn't enjoy and doesn't feel good about to this day—cost Alfred his job and his pension. Although her crime isn't severe, the punishment is heavy: Alfred's seemingly sudden decision to "change his mind and quit" (6.862) plays a huge role in the Lamberts' lives going forward.
Sometimes the smallest decisions have the biggest consequences.