I will likely change this review to five stars as I think more about what I’ve read.
The minute I finished the book, I went online to see what conclusions others had made about what Monica was meant to signify. If you do as I did, you will find a lot of very varied explanations. The only reasoning I could accept from others is the fact that there are pages of a different, more yellowed color, and that those were Monica’s stories.
Most of what this book is about is belonging - to people, groups, family, committed relationships. It is about a girl with a neglectful mother, who leaves her behind, and how that girl, as she goes through life, struggles with meaning. It is beautiful. At times tender. At others, terrifying.

In an interview, Clowes said:
“The book is in part about dealing with chaos, and it felt like chaos was and is reigning supreme.”

I know I will have to read it at least two more times, and I really did sit down with it and eliminated all distractions. It is a story to thick with details and meaning to be fully appreciated in one sitting. It is also heartbreaking.
I’m changing it to five stars.

A quote from an interview with Clowes:

I think about that a lot. Where does it all come from? What was I setting out to do? But it all just... happens. I had that "Pretty Penny" story kind of in mind. It was a story I had wanted to do for a long time, to try and capture the way my childhood felt, the craziness of it and the kind of inexplicable chaos of that era. And I was like, "I need a narrator for this story," and I realized, it should be through the viewpoint of Penny's baby. And so that's where it began. I had all these other stories in mind, but I wasn't sure it was even going to be the same character. And then, all of a sudden it started to gel, and I was thinking about periods in my own life that felt very separate from each other-- episodic almost, but somehow related, and I began filtering those emotions and experiences through this character, and all of a sudden I felt very free and I began to feel her coming to life and becoming her own person.