I needed a single book. I was told to go to a great building where they keep them all. I expected a merchant. I found something my homeland, in eight hundred years, never dared to build. A woman named Susan stood at a desk. "You got a library card? It's free. Takes two minutes." Free. I would be given a card, and with this card I could take a book — any book — out of the building, to my own home, and keep it. "For how long is it mine?" I asked. "Three weeks. You can renew it online if you need more time." Mine. For three weeks. On the strength of nothing but a card and my word that I would bring it back. In my land, a scroll of true value was chained to its shelf and guarded by a monk who slept beside it. Here, Susan handed me a book about volcanoes and told me to have fun. "Just bring it back when you're done, hon." That was all of it. No coin. No guard. No oath in blood. A nation that built a house of ten thousand books and lends them, one by one, to any stranger who promises to return. I took the book about volcanoes. I did not want a book about volcanoes. I took it because I could, and because trust unaccepted is trust insulted, and I read every page, and I now know a great deal about volcanoes. I returned it on time. Susan scanned it. The machine made a small, forgiving sound. "Thanks! See you next time." So. There is a next time. I have forty-one books at home now. …I have learned there is, in fact, a limit. It is not a limit of trust. It is a limit of how many books one man can carry to his car in a single trip. I have also learned what a "late fee" is. It is not a punishment. It is the gentle weight of a promise, measured in cents. I owe this building three dollars and twenty cents. I intend to honor that debt forever.