[There are spoilers so don’t read ahead if you haven’t finished!]
When he reminisces about Katherine XIX early in the novel, Colin says “She said I love you as if it were a secret, and an immense one.” This very thing he loves about Katherine XIX becomes the thing which connects him to Lindsey Lee Wells in the first place—she bites her thumb in front of him, a “private habit.” They become the people they most want to be around, the people you can think out loud in front of, the people that show you their secret hiding places.
Lindsey’s biggest insecurity is that she is never truthful. She says the only statement that’s true that begins with “I am” is “I am full of shit.” She has been faking everything for a long time, which is why when it’s finally over with TOC, she’s mostly relieved because she doesn’t have to pretend anymore. This is the relief she transfers into her relationship with Colin, someone with whom she had always felt like she could be private in front of. The sharing of private things throughout the novel (whether it was biting her thumb in front of him, or sharing the theorem with her, or sharing her hiding place, or thinking out loud in front of her—something introverted people like Colin simply don’t do—, or telling him how full of shit she is) is, again, what binds them together.
Now the reason Lindsey Lee Wells is better than all the other Katherines is how she makes him forget about all of them, especially Katherine XIX. What Colin discovers about his breakup with Katherine XIX is that “Dumping isn’t something that gets done to you; it’s something that happens with you.” It’s more like an inevitable coming of separation. The reason it didn’t work was because he was too needy and she was too inconsistent. She was a good person and kind, he says, but she lit up his heart a little too much. With his insecurity and her inconsistency, they were an obvious bad match but he didn’t notice because he had wrapped himself up in her. Lindsey helps him unravel.
In his final story, he also says, “You don’t remember what happened. What you remember becomes what happened.” It’s not about what happens it’s about what we remember happening that makes it matter. Later, in the epilogue he says that in a moment nothing may happen but it can still be thick with mattering. The affect is what matters. So, even being around Lindsey makes him forget things—that’s something worth noting. And further, forgetting is just the beginning because it allowed him to step back and look at his relationship with Katherine XIX, which just wasn’t right.
Most importantly, though, is that Lindsey Lee Wells is the one who teaches him storytelling. He even says that this is so much a part of how and why he loves her. She teaches him that mattering (his biggest insecurity) comes from telling stories. Again, it’s about affect. How we are changed by what happens to us is what really matters. And how we are changed is how we remember. Those are the stories of infinite meaning, the ones that make us matter. And further, she shows him we cannot be in the stories we have finished. The future is wide and expanding before us and in that, there is always the possibility of mattering—the ability to reinvent oneself, to transform oneself into something different, something even better.