What does Santiago detect in his father's gaze?

Santiago in The Alchemist can see in his father's gaze that his father sympathizes with him and has the same desires that he has.
Santiago was trained to be a priest, "but ever since he had been a child he wanted to know the world, and this was much more important to him than knowing God and learning about man's sins" (Coelho, 5). Santiago goes to his father to tell him that he wants to travel, and that he has decided to become a shepherd so that his job will allow him to do this. Although Santiago's father tells him that he will end up learning that the world is the same all over, and that eventually Santiago will come to the realization that he is already living in the best place in the world, Santiago can tell that his father sympathizes with him.
The next day, Santiago's father gives him some money and his blessing, and Santiago could see "in his father's gaze a desire to be able, himself, to travel the world—a desire that was still alive, despite his father's having had to bury it, over dozens of years, under the burden of struggling for water to drink, food to eat, and the same place to sleep ever night of his life" (Coelho, 5).
Santiago can tell that his father understands his desires, and this is the reason that his father supports him and allows him to go.