Music is approached and understood in many different ways.

Music theory is a way of mapping it all. When Sam hits that note without thinking, it's because he naturally feels how it will need to be sung--his body tenses in all the right places to hit that opening G without thinking about it. Music Theory allows us to name all the notes and chords and keys, and to write them in a language that others can decipher. All the "rules" are up to us.