The Rule of Thirds

From The Little Mermaid. I was noticing the focal point, the mouth of the cave is exactly at the intersection of thirds. Why is this a timeless rule. Any focal point at the intersection of thirds will NEVER cut the picture in half. There is either more above or below and more to the right or left. Never the same. By using values the background also uses an "O" composition. Dark at the edges getting lighter until the focal point which is the darkest dark next to the lightest light.

Wall Photos

By:Walt Disney Animation Studios

You can bet, though, that when the Little Mermaid is added to the picture she is lighter, has more contrast, more detail and more color than anything in the background. Because she is the real focal point.