I want to buy a book—perhaps it’s a specific book, identified in a review or mentioned by a friend, or perhaps simple intellectual restlessness has put me in the mood to browse a bookstore shelf and find something new. As I descend to the streets of the city where I live, I recall that many fine unread books remain on my overstocked shelves at home. I’m aware of them every hour of the day, even when I look up from the book I’m currently reading. They remind me of promises made to read them when they were bought; some of these promises are now decades old. My shelves also hold certain already-read volumes that deserve a careful, more mature rereading. I should turn back.