Well... I mean I did time it, haha. I know that spot and often go shoot there because of this great light. I conceptualized what I wanted (single person lit by the sunlight, surrounded by shadow). Then it was a matter of trial and error until the people arranged themselves just right (that's the luck part). But to get this, I had to stand in the same spot with the camera glued to my face for 5-10 minutes. The final moment is lucky, but all of the preparation is intentional.