The article explores the idea of externalities in economics, which are unintended effects on others from economic activities. It discusses how externalities were once seen as unimportant but are now gaining attention again. The researchers studied the history of how externalities were regarded in economics to understand their changing significance. They found that externalities were initially considered crucial, then became less important, and are now coming back into the spotlight. This shift in perspective on externalities highlights their impact on economic analysis.