Blind drawing will reveal to you your first impression of certain shapes. For example, in this portrait are the man’s long forehead and pointed tip of the nose, the widely opened mouth, and his low zygomatic bones. If you want to do a sketch which will take a much longer time with more details about, for example, a portrait, doing a fast sketch before you start can be a good way to catch your first impression of this individual (or an image of this individual).
