The guitar is a fantastic and extremely popular instrument. Many people can pick up a guitar and play a few chords, or sing one song. I strongly urge guitarists who comes to me to be interested in learning the musician aspects of the guitar as well. Most people who learn to play an instrument have to learn theory, scales, and harmony as well. On the guitar, you do not have to learn these things to be able to "play" the instrument but I urge people to because that will show in the music you make.