The author of the #1 New York Times bestseller The Anxious Generation shows how a deeper understanding of the world's philosophical wisdom can enrich and transform our lives "Wonderfully smart and readable." -- Washington Post In The Happiness Hypothesis , social psychologist Jonathan Haidt skillfully combines philosophical wisdom and scientific research to explore ten "Great Ideas" that have been discovered by several of the world's civilizations. In each chapter, Haidt questions a Great Idea in light of what we now know, and extracts from it the lessons that still apply to our modern lives, thereby illuminating the causes of human flourishing. Now with a new prologue, The Happiness Hypothesis expertly unravels the world's philosophical wisdom and its enduring maxims--such as "Do unto others as you would have others do unto you" and "What doesn't kill you makes you stronger"--and tackles the eternal question "How can I live a meaningful life?".