What makes a good Ruby on Rails developer?

I wrote about what makes a good JavaScript developer (not yet published) after researching the history of the language--the stigma around because of the way it was developed and also how it was made to be accessible like Visual Basic--and this makes JavaScript the world most popular language now. So I realized that it would take a "da Vinci" type of person to be a great JavaScript developer because you need to be both an engineer and an artist. But what about Ruby on Rails developers? What would make one good? Thanks for your thoughts!