ANSWER: It rips.
I did not learn that fact in graduate school, preparing to work with children. I learned it many years ago as a frustrated young artist with a ripped painting. We frequently hear warnings about this in the Museum art studio but, as with most things, humans learn best through their own trial and error.
Paper often gets too wet, red pastels are drawn on red paper and too many colors get mixed together resulting in multiple bowls of brown paint. While children may give an accurate answer to the eternal question of, “What do you get when you mix yellow and blue?” they don’t really learn what will happen until they sit down with the actual paints.
While experimentation may not result in masterpieces, real discovery about colors, materials and art processes happen everyday. The experience of ripping a painting by using too much paint results in learning to use less paint, and, ultimately, the ability to turn that experimentation into a real work of art.