The luck of Teela Brown. - Larry Niven

Why hadn't they built a lot of little Ringworlds instead?

Isn’t the history of human interaction the conversion of neighbors into enemies? Or into nonhumans, that we might deprive them of said chattels, or life itself?

"You look like a girl with a secret," Matt said. "I think it must be the smile."
She moved closer to him, which was very close, and lowered her voice. "Can you keep a secret?"
Matt smiled with one side of his mouth to show that he knew what was coming. She said it anyway. "So can I."