I call this "circling the drain" because we watch as our painting or drawing spirals right down into the sewer.
From observing my own process and also how my students sometimes get lost, I have found that this is the result of one single, simple problem, and there is one single, simple thing we can do to halt the downward spiral and salvage the work:
Easy enough, but it's amazing how often we all forget to look at our subject. Our tendency is to just stare at our own artwork and fiddle, which just makes the problem worse.
This is what I have posted in my studio to remind myself what to do when I get lost:
This is what I mean by each of these:
We naturally tend to zoom in our vision, narrow our focus, and look at tiny areas. Then we inch our way around the subject as if we are drawing by looking through a drinking straw. This makes mountains of molehills; literally, small variations on a contour are magnified when we zoom in. It also tends to make us exaggerate differences in value, so we make a dark patch too dark and a light patch too light.
The key is to back up and look at your artwork and your subject with large vision, comparing every part to every other part instead of focusing on small areas. Scan for the largest shapes, move your vision around often: if you are drawing a figure's head, move down and draw the feet for a while. Compare values deeps in the shadows to values far away in the light areas. Draw the whole, not the parts. Think big.
We all have a tendency to hunker behind our easels with our nose to our own artwork. After a while, we forget to ever peek around the easel at all and we end up drawing or painting essentially from our imagination. But if you discipline yourself to make a mark and LOOK before you make another mark you will suddenly find the painting or drawing flying along easily, growing magically from under your brush or pencil. Mark, look, mark, look, mark, look.....
When we are really, really lost, sheer panic sets in. That's when we have the urge to keep working faster and faster, and the artwork falls out of control at an alarming rate. When I get really, really lost I put down my brush and just stop and look at my subject. Then I bounce my vision between my subject and my artwork, back and forth, without ever making a mark. The longer I can discipline myself to look without making a mark at all, the clearer it becomes what needs to be adjusted. I tell my students to put down their charcoal and make a mental list of THREE things to change before they pick up their charcoal again.
A note on self deception:
Sometimes a piece of artwork is falling out of control but we can't admit it. We are too attached to the work we have already put in, and we want the artwork to be better than it is. This is where integrity comes in: the artist must hold themselves to the highest standard, otherwise no learning or exploration is happening. If we tell ourselves our art is "good enough" it isn't. That is self-deception.
To be art, it must be better than "good enough".
Do what it takes to learn and get better with every mark of every piece. Otherwise, we may as well go find a less demanding endeavor. Why be an artist, if not to get better?