What about the blues? Well, blues is an attitude inside, which is melancholy. Blues is a heritage of black people, and when a black man (or woman) is within melancholy, his (her) skin from brown turns to blue. In music, everything start with a percussive way to play guitar, which soon shifts in a virtuoso way to play with no reference to European tradition. Then mixing the cultures, it becomes the prevalence of rhythm over harmony (percussion over chords). Essentially, it’s to play music both in case you know nothing of music’ theory or even when, knowing it all, you can do what you want.
One more last thing: blues is freedom in music (jazz & rock come from it!)