Why was The Stone Breakers considered a Realist painting?

The Stone Breakers (1849) is considered a quintessential Realist painting because it represents a radical departure from the idealized, controlled subjects favored by the Neoclassical and Romantic schools of the time.1

The work is defined as Realist for the following reasons:

• Subject Matter: Instead of depicting aristocrats or mythological figures, the painting focuses on the humble, unadorned lives of the working class, specifically two peasants performing physical labor in a barren rural setting.1
• Rejection of Idealization: Gustave Courbet did not attempt to glorify or embellish his subjects. By presenting them in a bold, stark manner, he challenged the prevailing artistic conventions that demanded beauty and refinement in art.1
• Commitment to Truth: The painting reflects the core Realist philosophy of depicting contemporary life accurately and without artifice. It serves as a "realistic rendering" that prioritizes the honest observation of material conditions and the physical reality of the common man over contrived idealism.21