Learning to Draw: Chair

This morning I was caught drawing. A chair. A woman on her cellphone kept looking at me. Finally I showed her the chair, a brown-stained wooden thing in bright sun (alternating with raincloud) next to a silver pillar. Downtown Regina, Scarth street mall.
Seeing how I'd handled the darkness and lightness in the chair itself, never mind everywhere else, the woman looked away without the usual looking back. I attempted to show the chair closer than the tiled floor it stood on. I tried to disguise the chair's outline.
If she wanted, I'd try to make the chair not look so flat, but why am I still talking about her.
I found it easier to compose a list of other things impossible to draw, which includes rain, two girls running through it, my annoyance at cars parked on a pedestrian mall, a man's pronation in cheap shoes, and the woman's decision to stand up from her own chair.
Further darkening failed to bring her near.