Photograph of a Stranger

I stumbled upon this man while admiring the art that he displayed on one of the park's fences. When I went up to him to talk, I asked him if he was the artist. He said "yes" and proceeded to show me a silver sharpie, a pen, and his sketchbook.
Then he asked me to name an instrument, and I kindly said, "A guitar".
He picked up his silver sharpie, flipped to a blank sheet in his sketchbook, and started drawing.
What amazed me the most was that he never picked his pen up from the paper, and that he had already had an idea of how to map out the design.
When he was finished sketching, he lifted his sketchbook up and revealed his finished product: a man with a guitar.