As we arrive at the ninth and final chapter, let's note that there's something special about the number nine. Dante's inferno consisted of nine levels. The Norse cosmology comprises nine worlds. The Greek hydra boasted nine heads. Sauron deceived nine human kings with rings of power in Tolkien's The Lord of the Rings. Adherents of the pseudoscientific Enneagram assert nine personality types. Our happiness, in the English expression, lives on “cloud nine.” Ferris Beuller's high school recorded him absent nine times (before he hacked into its computer to change it). More relevant to the thesis of this book, we mentioned nine environmental systems that must be kept within quantifiable limits for humanity to endure indefinitely, according to one famous ecological science article.1 Hinduism reveres the number nine as the perfect end to a cycle: the last single numeral before a change in the order of magnitude in a base-10 number system, bringing with it wisdom and fulfillment. Perhaps relatedly, Mnemosyne, the Titaness personifying memory in ancient Greek mythology, was associated with the number nine, as well as with all things that memory makes possible: the progression of history, the growth of knowledge, the development of art. After lying with Zeus for nine straight nights, Mnemosyne bore the nine muses, who in turn nurtured the nine creative arts—those acts of generation that seem like they come from thin air (or from the heavens), but perhaps represent radical upgrades in the organization of our previous modes of sharing ourselves and cultivating empathy. Fitting, then, that we come to rest here, at the cusp of radical upgrade—one predicated on a long progression that foreshadows change to come.