If I had a camera," I said, "I'd take a picture of you every day. That way I'd...

If I had a camera," I said, "I'd take a picture of you every day. That way I'd remember how you looked every single day of your life." "I look exactly the same." "No, you don't. You're changing all the time. Every day a tiny bit. If I could, I'd keep a record of it all."
"If you're so smart, how did I change today?"
"You got a fraction of a millimeter taller, for one thing. Your hair grew a fraction of a millimeter longer. And your breasts grew a fraction of a-" "They did not!" "Yes, they did."
"Did NOT."
"Did too." "What else, you big pig?"
"You got a little happier and also a little sadder."
"Meaning they cancel out each other, leaving me exactly the same."
"Not at all. The fact that you got a little happier today doesn't change the fact that you also become a little sadder. Every day you become a little more of both, which means that right now, at this exact moment, you're the happiest and the saddest you've ever been in your whole life."
"How do you know?"
"Think about it. Have you ever been happier or sadder than right now, lying here in this grass?"
"I guess not. No."
"And have you ever been sadder?"
"No."
"It isn't like that for everyone, you know. Some people{...}" "What about you? Are you the happiest and saddest right now that you've ever been?"
"Of course I am."
"Why?"
"Because nothing makes me happier and nothing makes me sadder than you.