As the title says, a really great shot is equal parts luck and skill. The cat in this photo was sheer luck. But then for several years I stared at the photo, trying to make it work. (The original had a much broader scene.) I kept trying to crop it, or shift the contrast, or ... or... something! Sometimes it's hard to step back from a detail that I really like to see how a composition works as a whole. I loved the cat and the incredible blue walls, and didn't want to lose either. That made it very hard to see the photo as a whole. The angle of the cat's head, and the glaring white wall made it hard to figure out where the center should be. Finally I realized that the verticals (see those long brown lines?) were the key to organizing the composition, and as I cropped it to move the dark slit of a doorway toward the center, it came together.
It's really a wonderful feeling when you've struggled with a composition, and suddenly with just the slightest adjustment, it all slides into place. I still wish I could go back and ask the cat to move 4 inches to the left and look at the camera. He probably didn't speak English though.