One of the most famous concepts in street photography is “the decisive moment,” a term originated by Henri Cartier-Bresson. It is what separates the small percentage of great street photos from the rest. The idea is to capture someone in an action, pose or gesture that creates tension, humor, suggests a story, or simply creates beauty.
When I shoot in the street my first instinct is to look for pairs of people. They are more likely to be engaged with each other, and therefore create that sort of moment. It can happen in larger groups, or with solitary people to be sure, but pairs of people seem to pat off at a higher percentage. When I saw these 2 young women approach I tracked them as they were rather actively engaged with each other as they walked across the street, and just as I decided to shoot, one of them dropped her purse, and turned back to pick it up.