Lines are everywhere man. Either implied (lines of a silhouette against a background) or explicit (a scar, a falling rain drop, a wrinkle, a closed mouth). One way - maybe the best way - to define a shape, say a square, is by the lines that contain it. Kinda see what you're getting at, but don't neglect the simple and effective line, it really just heavily depends on the context and how you draw the line. For example, beginners will often draw a portrait with a very hard and dark lines on the face and around the mouth, which ages the subject. Consider where Holbein uses lines and doesn't and follow his example.
