There were many lines in Paper Towns that struck me, but I'll share with you what might be my favorite, which occurs right before Margo and Quentin part for good.  He talks a great deal about the metaphors that could be applied to relationships and then says,

..."[E]ach of us starts out as a watertight vessel.... And the vessel starts to crack open in places....But there is all this time in between when the cracks start to open up and when we finally fall apart.  And it's only in that time that we can see one another, because we see out of ourselves through our cracks and into others through theirs" (302).

Quentin's central problem throughout the book is that he idolizes Margo, which prevents him from seeing her clearly, as she really is.  She is not a goddess, just a teenage girl who is struggling to grow up and be her own person, much as Quentin is, and as every adolescent is.  His love for her has been blind since the book's beginning.  And the book is really a journey to understand himself and to understand Margo.  He can now see her cracks, and this journey, his quest for her, has given him a few of his own. It is now that he is able to truly see her as she is, a flawed, cracked human being, just as he is.  Cracks make people vulnerable, but they also make them open, open to understanding another, open to empathizing with another, open to love, rather than blind worship.  Margo is a cracked vessel, and unless and until Quentin can accept her as she is, there can be no basis for real love. 

When I came to this section of the book, it also reminded me of a charming little story about another cracked vessel, the link for which I have included below. I invite you to read the story, which might enrich the quote from the book even more, as it did for me.