“The human mind wants to worry. This is not necessarily a bad thing—after all, if a bear is stalking you, worrying about it may well save your life. Although most of us don’t need to lose too much sleep over bears these days, modern life does present plenty of other reasons for concern: terrorism, climate change, the rise of A.I., encroachments on our privacy, even the apparent decline of international cooperation.In his fascinating new book,21 Lessons for the 21st Century, the historian Yuval Noah Harari creates a useful framework for confronting these fears.While his previous best sellers,SapiensandHomo Deus, covered the past and future respectively, his new book is all about the present. The trick for putting an end to our anxieties, he suggests, is not to stop worrying. It’s to know which things to worry about, and how much to worry about them. . . .Harari is such a stimulating writer that even when I disagreed, I wanted to keep reading and thinking. . . . [Harari] has teed up a crucial global conversation about how to take on the problems of the twenty-first century.”—Bill Gates,TheNew York Times Book Review