If you're here for Street Photography 101, sit down and open your books to Cartier-Bresson's "The Locks at Bougival." Yes, Henri's composition is fabulous, as usual. But you might also notice that this picture slaps you across the head with a message about the human condition (tragic how that phrase has become a cliché). It's the human condition part that makes it an effective street photograph, not the magnificent composition. The composition is simply expected, just as the floor in your house is expected.
But Rob's got an important point. Every really good street photograph I've seen is a (candid) snapshot, meaning it's not something you can set up. Yes, Doisneau used to set up some of his "street" shots. But once you internalize street photography, Robert's fakes begin to come across as fakes, even his famous "Le baiser de l’hôtel de ville," though he had some good actors to carry out the action for that one. In the end it all comes down to HCB's dictum: "Photographing is nothing. Looking is everything." And being ready to grab a snapshot that tells you something about the human condition is the rest of it.