Yes you're right. I think what happens is I get lazy when it comes to the shading. I don't want to take the time to do it. And I get sloppy. I also enjoy the contour portion because it seems the most interesting and in focusing on it too much, I lose the form.
Yeah- and using black and white to get highlights and shadows. It helps some people to work from a mid tone out. Forces you to focus on the whole range.