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