The charcoal pencil was the medium that gave me the AHA moment. I got a pretty nice pastel set as a birthday gift from my wife. This was the time I had no idea how to do a painting in colors and thought, wrongly, that I knew how to draw. So, I searched for a private class in Maryland and found this very talented teacher. Talked to her on the phone and met at her studio. She asked me to show what I have been drawing and that where I was told that my "good" drawing were not that good. At least, it didn't have the character and depth.
First class, she sets a white ball on the table with a direct light on it and ask me to draw it. She gave me a charcoal pencil and left me alone for a while. Here I am looking at the white ball and saying to myself "how the heck you draw a WHITE ball with a black pencil". Did my best and thought again that the results was not that bad. WRONG.
Then she showed me The Technique, which consisted of identifying the middle tones, hightlight, dark side, cast shadow, etc. Then she asked again to draw the ball but now using this technique. That's when the ball came to life and you could swear it was 3D without the need of these funky glasses. AHA!