Shortly after 335 B.C., within a newly built library tucked just east of Athens’ limestone city walls, a free-thinking Greek polymath by the name of Aristotle gathered up an armful of old theater scripts. As he pored over their delicate papyrus in the amber flicker of a sesame lamp, he was struck by a revolutionary idea: What if literature was an invention for making us happier and healthier? The idea made intuitive sense; when people felt bored, or unhappy, or at a loss for meaning, they frequently turned to plays or poetry. And afterwards, they often reported feeling better. But what could be the secret to literature’s feel-better power? What hidden nuts-and-bolts conveyed its psychological benefits?