He has the strangest expression on his face—the emotive equivalent of 404 - Robin Sloan

San Francisco is a good place for walks if your legs are strong.

Sometimes, you’re stuck with a system too complicated to model completely.

"Neel cuts in: "Where'd you grow up?"
"Palo Alto," she says. From there to Stanford to Google: for a girl obsessed with the outer limits of human potential, Kat has stayed pretty close to home.
Neel nods knowingly. "The suburban mind cannot comprehend the emergent complexity of a New York sidewalk."
"I don't know about that," Kat says, narrowing her eyes. "I'm pretty good with complexity."
"See, I know what you're thinking," Neel says, shaking his head.
"You're thinking it's just an agent-based simulation, and everybody out here follows a pretty simple set of rules" — Kat is nodding — "and if you can figure out those rules, you can model it. You can simulate the street, then the neighborhood, then the whole city. Right?"
"Exactly. I mean, sure, I don't know what the rules are yet, but I could experiment and figure them out, and then it would be trivial — "
"Wrong," Neel says, honking like a game-show buzzer. "You can't do it. Even if you know the rules — and by the way, there are no rules — but even if there were, you can't model it. You know why?"

My best friend and my girlfriend are sparring over simulations. I can only sit back and listen.

Kat frowns. "Why?"
"You don't have enough memory."
"Oh, come on — "
"Nope. You could never hold it all in memory. No computer's big enough. Not even your what's-it-called — "
"The Big Box."
"That's the one. It's not big enough. This box — " Neel stretches out his hands, encompasses the sidewalk, the park, the streets beyond — "is bigger."

The snaking crowd surges forward."