I'd say and others have said:

"when all of the elements come together to form an image that reveals a stop in time with a true candid moment that can never be recreated, you
have potentially captured the decisive moment. if one part of the image was removed or if the photgrapher had shot a moment earlier or later it
would not be there." Also: "I take it to mean the moment when the elements of the picture come together to make the pictue and tell a story. This implies something that's changing."