Mystery to Me
One of the photographic limitations of the iPhone is that it has limited dynamic range compared to film or even a digital camera with a larger sensor. That's OK with relatively even lighting, but in bright sunlight with strong shadows, it leaves you in a difficult place: Either you expose for the highlights and risk losing shadow detail, or you expose for the shadows and risk blowing out the highlights. You can compensate for this in post processing, but for a quick shot on a sunny day it can be a drag.
One of the cool things about photography is that technical limitations can often be flipped so that they're features, rather than bugs. Sometimes it's a good idea to let shadows go black, even cranking up the contrast a bit, in order to to give dramatic impact to an image. Especially in black and white street photography, there's a long tradition of photographers going this route, of using shadows to set up strong contrasts between light and dark.
If you want to experiment with this, a good time is on a bright, sunny day, late in the afternoon when shadows are longer. I did some experimenting late yesterday afternoon on Monroe Street. This was the result.