Art can be messy at times, but some of the messes are not so desirable. I remember professors telling me I was overworking the surface of my art and muddying it up. This was not my intent, but my choices(poor choices) led to this unfortunate outcome. It often occurs when one adds too much, too many ideas, too many colors, too many brush strokes, and creates a "muddy" area in their work. It comes from rushing. It comes from lack of vision for the end product. It comes from inexperience. It comes from not knowing when to stop. It comes from being stressed. It comes from being tired. No one intends to make their work appear muddy, but it happens. Though most artists will move beyond these mistakes as they grow/mature in their work, there are a number of factors that can cause one to still muddy things up from time to time.
I wait for the Lord, my whole being waits, and in his word I put my hope.