Henri Cartier Bressson thought in order to get a decisive moment photograph you have to capture it quickly because that is the most authentic and “real” moment. He also believes that when taking a photograph you should not think too hard about it because the point comes by itself.
Before capturing the photo quickly, he has thought about the photo. He has probably moved into a position where when he shoots the elements that he wants to compose will be in the frame. He is working intuitively and has developed his vision by shooting a lot and seeing what works and what doesn’t