WHAT IS YOUR FAVORITE DEEP, ELEGANT, OR BEAUTIFUL EXPLANATION?
Scientists’ greatest pleasure comes from theories that derive the solution to some deep puzzle from a small set of simple principles in a surprising way. These explanations are called “beautiful” or “elegant”. Historical examples are Kepler’s explanation of complex planetary motions as simple ellipses, Bohr’s explanation of the periodic table of the elements in terms of electron shells, and Watson and Crick’s double helix. Einstein famously said that he did not need experimental confirmation of his general theory of relativity because it “was so beautiful it had to be true.”
Since this question is about explanation, answers may embrace scientific thinking in the broadest sense: as the most reliable way of gaining knowledge about anything, including other fields of inquiry such as philosophy, mathematics, economics, history, political theory, literary theory, or the human spirit. The only requirement is that some simple and non-obvious idea explain some diverse and complicated set of phenomena.