Economics was known as the "Dismal Science" because

More than a century and a half ago Thomas Carlyle defined the economy as "dismal science." This term is born from the implicit pessimism of the ideas of economist Malthus about the difficulty of growing food production at the same rate as population expansion.

More recently, Samuelson placed the origin of the discipline's sadness on the idea of budgetary constraints that would always place us in the face of confrontation between our desires and our possibilities of serving them.

It is also claimed that John Stuart Mills propitiated this term given that institutions, not race, determined why one nation became rich while others did not.