"Beauty is in the eye of the beholder" may be more of an exception than a rule. Whether we can or cannot articulate the reason why something is beautiful (or not beautiful), we generally agree on what is and is not beautiful.

The Naked Mole Rat is certainly not the most beautiful of creatures. Those few of us who think that it is are the exception. The puppy, full of fur, is probably more pleasing to most of our eyes than the Mole Rat.

On the other hand, Rainbows and smiley face sunsets are generally considered to be beautiful. Why? It just is.

Given that we all generally agree upon what is beautiful, there are certain rules and conventions about photography and lighting that can make our photographs more pleasing to the eye of the many beholders.

Here are a couple of paintings by Rembrandt, a 17th century painter. Notice the lighting and, just as important, notice the shadows.
Naked Mole RatPortiaPonto Beach Sunset RainbowSmiley Face Sunset :)Golden Ratio RectangleRembrandt lighting