How do Santiago's thoughts and perceptions about himself and the world begin to change in The Alchemist?

Without a specific location in the book, this question could be asking about a couple
of times in Santiago's life. Readers are told that Santiago wasn't always a shepherd. He was
supposed to be a priest, but early on in his childhood, the desire to travel and see the world
became a driving force in his life. Getting the courage up to tell his parents these feelings is
a change in Santiago.

His parents had wanted him to
become a priest, and thereby a source of pride for a simple farm family. [. . .] But ever since
he had been a child, he had wanted to know the world,...