When working on a painting like this, I often think about detail. How much detail goes into the section I am working on? You want enough detail to tell the story but not so much that it pulls focus from the main theme. The difference between the two is a very fine line.
If I had painted every outside line of the cobblestones into the background, you would not as readily notice the open violin case. If the people in the distance had sharp edges and lots of detail, your eyes would be drawn to them and linger there.
By the way, I had a blast painting the violin case. Those purple-y velvet colors are uncommon for my normal wildlife palette.