"Here's the thing about Hazel: Almost everyone is obsessed with leaving a mark upon the world. Bequeathing a legacy. Outlasting death. We all want to be remembered. I do, too. That's what bothers me most, is being another unremembered casualty in the ancient and inglorious war against disease.

I want to leave a mark.

But Van Houten: The marks humans leave are too often scars. You build a hideous minimall or start a coup or try to become a rock star and you think, "They'll remember me now," but (a) they don't remember you, and (b) all you leave behind are more scars. Your coup becomes a dictatorship. Your minimall becomes a lesion.
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We are like a bunch of dogs squirting on fire hydrants. We poison the groundwater with our toxic piss, marking everything MINE in a ridiculous attempt to survive our deaths. I can't stop pissing on fire hydrants. I know it's silly and useless--epically useless in my current state--but I am an animal like any other.

Hazel is different. She walks lightly, old man. She walks lightly upon the earth. Hazel knows the truth: We're as likely to hurt the universe as we are to help it, and we're not likely to do either.

People will say it's sad that she leaves a lesser scar, that fewer remember her, that she was loved deeply but not widely. But it's not sad, Van Houten. It's triumphant. It's heroic. Isn't that the real heroism? Like the doctors say: First, do no harm.

The real heroes anyway aren't the people doing things; the real heroes are the people NOTICING things, paying attention. The guy who invented the smallpox vaccine didn't actually invent anything. He just noticed that people with cowpox didn't get smallpox.
...
But then I wanted more time so we could fall in love. I got my wish, I suppose. I left my scar.
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What else? She is so beautiful. You don't get tired of looking at her. You never worry if she is smarter than you: You know she is. She is funny without ever being mean. I love her. I am so lucky to love her, Van Houten. You don't get to choose if you get hurt in this world, old man, but you do have some say in who hurts you. I like my choices. I hope she likes hers.”