Paul Cézanne saw the world as planes — little flat patches that build a mountain like bricks build a wall. Young Picasso and Braque studied him and pushed the idea to its edge: shatter the scene into facets and show every side at once. They called it Cubism, and it started with Cézanne's patches.
Your canvas is now fractured into invisible facets. Strokes stay inside the facet they start in, and each facet shades your color differently — paint ACROSS the lines and watch the picture shatter into planes, like Cézanne's mountain.