I always believed that drawing with pencil is way more difficult than painting with brushes and paints. Unlike the painting, drawing with pencil is a little bit different and it requires special skills. It requires from artist to be very precise. One of the most important skills which artist has to acquire in order to be a god in pencil drawing is regulation of the pressure on a pencil while drawing.
Drawing realistic artworks with pencil only is even more difficult but following collection of photos will show you how remarkable it can be when it is done properly.