- In spite of being raised by an emotionally abusive misogynist father, Nick and Margo have had a close and loving bond all their lives. The events of the book - in particular, Margo finding out that Nick has cheated on his wife - not only strains their relationship, but strains it in ways that clearly brings to mind their upbringing. At one point, Nick notes that whenever Margo looks at him, part of her now sees "another worthless man taking up space," and whenever he looks at her, part of him now sees "another petty woman judging him."
- Their relationship is particularly clear in the scene right near the end when Go is having a complete tearful breakdown as she realises that much as he hates her, part of Nick really does want to stay with Amy. Her shocked bafflement that her beloved brother does actually intend to "play house with that thing" rather than get the hell out as soon as it's safe is heartbreaking. That she follows it up with a Heartwarming Moment by promising to stand by him anyway does not detract from the tragedy.
- Desi may have been totally nuts, but he just looks so shocked and terrified when Amy kills him. It's hard not to feel bad for the poor guy, especially considering he didn't just die right away, but instead bled out (for about a minute, according to Amy in the book), staring Amy right in face as she watched him die in cold blood. As Nick puts it in the book, "A minute is a long time to know you're about to die."
- The reason Nick's father's (blue) house is called "the brown house" by Amy and Nick. When Nick was a child, he used to pretend that the reason his father never saw him and Go and rarely called them was because he was really a secret agent named Mr. Brown that had to pretend he didn't have a family. In his narration, Nick mentions Amy actually tearing up when she hears this story. It's somehow made worse when Nick says he didn't intend for it to be a sad story when he told her — he meant it as a "kids are weird" story, and didn't realize just how sad it was until he told someone else.
- The fact that, out of everything, what really breaks Nick's heart is the realization that Amy was never pregnant, and just made that up as part of the scheme. In spite of all Amy did to him, he genuinely wanted that kid. It's hard not to pity him a little in that moment.
Tear Jerker / Gone Girl