Why is it said that Cézanne subverted the classical realism of Western painting?

Classical realism seeks realism, like a photographic effect; what makes Cézanne different is that he didn't seek realism because he focused on the study of light, to identify the elements and laws that make up various kinds of light. What you see on his paintings are clumps of color, he strengthened the composition of the various base colors, but if you stand at a distance but found that these clumps began to merge, to the point of appearing natural and realistic, more accurate understanding and grasp of the effect of light and shadow in nature.

Cézanne can be called the pioneer of Impressionism, later Impressionist painters, such as Monet, Pissarro, etc., also inherited his ideas, focusing on the analysis of color, to create strange color effects, and more expressive.