Realism arose as an opposing idea to Idealism and Nominalism. Idealism is the approach to literature of writing about everything in its ideal from. Nominalism believes that ideas are only names and have no practical application. Realism focused on the truthful treatment of the common, average, everyday life. Realism focuses on the immediate, the here and now, the specific actions and their verifiable consequences.
Realists are concerned with the effect of the work on their reader and the reader's life.
This is a pragmatic view. Pragmatism requires the reading of a work to have some verifiable outcome for the reader that will lead to a better life for the reader. This lends a ethical tendency to Realism while focusing on common actions and minor catastrophes of middle class society. Realism aims to interpret the actualities of any aspect of life, free from subjective prejudice, idealism, or romantic color. It is in direct opposition to concerns of the unusual, the basis of Romanticism.