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, and this was much more important to him than knowing God and learning about man's sins. One afternoon, on a visit to his family, he had summoned up the courage to tell his father that he didn't want to become a priest. That he wanted to travel.

His dad actually gives Santiago his blessing and some money. His father also recommends becoming a shepherd because they are migrant by nature, and Santiago thinks that the job is wonderful.

The world was huge and inexhaustible; he had only to allow his sheep to set the route for a while, and he would discover other interesting things.

These feelings of contentment about his sheep and his job start to change after having dreams of treasure. The gypsy woman helps push Santiago toward belief in the treasure, and Melchizedek helps affirm the notion of going after a Personal Legend. Once his journey begins, Santiago's thoughts about himself waver back and forth about whether or not he actually can achieve his personal legend and the treasure. Santiago also believes through much of the story that the treasure is monetary; however, he will finally realize that the ultimate treasure is love, and he loves Fatima.