John Green's Turtle's All the Way Down is rich in the use of simile, particularly in order to explain an individual's lived experience and emotions.
One such simile touches on love, a central theme within the novel:
It’s a weird phrase in English, in love, like it’s a sea you drown in or a town you live in. You don’t get to be in anything else—in friendship or in anger or in hope. All you can be in is love.
In this quote, Green explores the concept that love is fundamentally different than other emotions that people experience and that the English language has evolved to reflect that. The simile "like it's a sea you drown in" alludes to the overwhelming, and sometimes threatening, intensity of love. This is because drowning happens when water from the sea begins to fill a person's lungs, just as love for another person can become inextricable from the concept of self.
Indeed, the concept of self is another important theme of the novel and appears in several similes, such as this one:
There's no self to hate. It's like, when I look into myself, there's no actual me—just a bunch of thoughts and behaviors and circumstances. And a lot of them just don't feel like they're mine. They're not things I want to think or do or whatever. And when I do look for the, like, Real Me, I never find it. It's like those nesting dolls, you know? The ones that are hollow, and then when you open them up, there's a smaller doll inside, and you keep opening hollow dolls until eventually you get to the smallest one, and it's solid all the way through. But with me, I don't think there is one that is solid. They just keep getting smaller.
In this quote, Aza examines the fragility of her concept of self; how can a defined self exist if she feels as though she isn't in control of her own thoughts or actions? The simile of the Russian nesting dolls is similar to the motif of the spiral, wherein Aza's thought spiral is described as continuing infinitely while also narrowing infinitely. However, the Russian nesting dolls also incorporate the way in which Aza eventually comes to terms with her concept of self. By the end of the novel, Aza has accepted that she is actually a plurality of selves, but these pluralities can still exist in one unified self, just as any one Russian nesting doll will contain multiple selves within it.