This paper explores how mergers may not always be good for everyone. They looked at a model where firms make similar products, and they found that a merger can make customers happy but not help society overall. It happens when small, not very efficient companies join forces and make the market less competitive. This kind of merger is called a "runner-up merger." So, even if shoppers benefit from lower prices or better products, society might suffer when competition decreases due to certain types of mergers.