Breaking news! Sources say American journalism exploits our negativity bias to maximize profits, and social media algorithms add fuel to the fire. Stephen Dubner investigates.

According to a decades-long research project, the U.S. is not only the most individualistic country on earth; we’re also high on indulgence, short-term thinking, and masculinity (but low on “uncertainty avoidance,” if that makes you feel better). We look at how these traits affect our daily lives...