I’ve been giving some thought to "The Decisive Moment," the title chosen for Cartier-Bresson’s ground-breaking, 1952 book by his American publisher. I agree with critics who see it as a poor choice words because it misleads us, implying that a distillation of reality is captured in such a moment.
In France, the elegant little book was titled, "Images à la Sauvette." Translated colloquially, it means "Images on the Run," which is a more expansive concept. It allows us to consider a fleeting facial expression, for example, or momentary body language.
Great street photos, or any great photos "caught on the run," achieve their vaunted status by evoking human emotions, such as humor or pathos. They may in some sense be "decisive," but that’s immaterial. It’s their evocative content and composition that make them great.