“You can tell who are the phonies by listening to people singing the protector’s songs. Only the songs with soul are his and were taught by him. The others are copies of other men’s songs. People are sometimes as deceitful as that. They sing someone else’s songs without even knowing what the songs say.”

A conversation between don Juan Matus and Carlos Castaneda, from The Teachings of Don Juan: A Yaqui Way of Knowledge

The context of the above quote is a conversation between don Juan and Carlos about the unique song(s) taught to an individual by Mescalito. I find a more general truth being discussed here: that it is obvious when songs (and maybe other aspects of our self) are devoid of soul and/or stolen from others.