Your source material is the people you know, not those you don't know, but every character is an extension of the author's own personality.
“Creativity is allowing yourself to make mistakes. Art is knowing which ones to keep.”
“A human being has so many skins inside, covering the depths of the heart. We know so many things, but we don't know ourselves! Why, thirty or forty skins or hides, as thick and hard as an ox's or bear's, cover the soul. Go into your own ground and learn to know yourself there.”