Line drawing is the most important, hence the most difficult to master of all the disciplines in figurative art.
Most painters and sculptors are lousy at drawing. I guess they feel as if drawing is just a step towards the end result (which is true but it doesn't need to be)
It's a shame because if they'd learn how to draw, their work could gain greater insight and even more depth.
When I paint I solve complex foreshortening issues with specks of certain colors, in drawing I can't hide my ignorance behind cheap tricks.