Henri Cartier-Bresson defines "The Decisive Moment" as follows:
"There is a creative fraction of a second when you are taking a picture. Your eye must see a composition or an expression that life itself offers you, and you must know with intuition when to click the camera. That is the moment the photographer is creative. Oop! The Moment! Once you miss it, it is gone forever."
However, Henri Cartier-Bresson didn't only take one single photograph when he saw a decisive moment ready to happen (David Hurn refers to this as a "pregnant moment") but rather took several images of the same scene.
That truth is reinforced by the fact that "Gare" is one of only two photographs I know of that Cartier-Bresson cropped. There was a fence off to the left, and he didn't have time to move to the right before it was time to shoot.
You can see the original, un-cropped version in his book, Henri Cartier Bresson: Scrapbook.
If you look carefully at the masters work like Cartier-Bresson, Elliott Erwitt, or Robert Frank you'll realize that the best of them are snapshots: raw reactions to what they saw before them, not planned intersections with the scene. There's no way HCB's conscious mind could have registered all the elements of the scene in "Behind the Gare St. Lazare" before he hit the shutter.
But experience, doing mental framing in your day-today life, and sticking to one focal focal length are crucial in this part.
And you can compare to the present, when nobody shots only one shot. You capture the moment that caught your attention the best way you can, and then, if you get the chance, you recompose and give it one more try or perspective.
I have no problem in revealing that
was the moment that caught my eye, but I choose the next composition
Getting access to the contact sheets, which are pieces of photographic paper onto which several or all of the negatives on a roll of film have been contact printed, of renowned photographer allows you to see how the decisive moment developed, and how it was selected from a set of images taken at each location.
This is not only related to the Masters, the modern street photographers do the same, but it's too early to disclosure this kind of information.
All this does not diminish the merit in any way, but unveils a myth and leads to a very encouraging thought: street photography is not an exact science!
There is no "right" or "wrong" way to shoot street photography, or as Winogrand stated: "There is no special way a photograph should look."
So, the real questions are: am "I" stating humanity, is it within reach, am "I" projecting a message, am "I" capturing people being people? ...