A street portrait succeeds most often by opening an unobstructed view into humanity. It offers the chance to observe at length other human beings in their natural state that is otherwise not possible.
Because we share so much in common, there’s an instinctive impulse to observe and analyze other people, strangers especially. Yet no more than a glance is permitted; anything beyond a casual passing look will likely be considered an intrusion if not a perversion.
But a photographic portrait whose unreserved emotion was captured spontaneously, and is now displayed on a screen or on paper, is safe to examine. So go ahead and stare, wonder, speculate for as long as you please, for as long as it takes to figure it out.