Rigor

I was asked today, What does elegance and beauty have to do with rigor? During my Beautiful Theories post, I included rigor when discussing the beauty and elegance of a theory. I didn't know why I threw that in either at first. I've stated that "simplicity is elegance". I believe that is true. When a statement or argument is simple, almost 'commonsense', it is difficult to defeat. It has already been reduced to it lowest constituents. It's balanced. It gives that feeling of "Eureka!" That same feeling that many of us get when we experience a defining moment, like when we see someone who is so beautiful we start to melt. Things that are elegant are simple; they leave no doubt about their beauty. That's rigor.