The first thing that came to my mind is the so-called "sonder" - the realization that each passerby is a unique and complex human being on their own, with their own worries, backstory, hopes, dreams and fears. We start off looking through our own window, and what do we see? Almost nothing. But even if we do not see something or someone at a first glance, it doesn't mean they are not there.
Very intimate portrait of human's psyche and their worries.