I think I need to clarify something: he's clearly trying to do lineart with those scribbles, which is what you shouldn't be doing
its one thing if you're just doing a sketch/gestural drawing but if you scribble it in when you're finishing a drawing, like a pencil sketch:

you're going to get this, where the outlines are all way too dark and rough, and the whole thing is hyper contrasted

if you use long flowing strokes you SHOULD be getting an effect like this
(as if it needed to be said: second is not mine
)