In Paulo Coelho's The Alchemist, the alchemist chooses Santiago over the Englishman to be his pupil or "disciple" because the Englishman believes that wealth in the world is found in gold. He believes that if he reads enough books and talks to the right people (like the alchemist), he will be successful. The Englishman does not recognize that each person has a Personal Legend and he cannot make himself listen to or recognize the universal language—he does not see omens or hear nature speaking to him.
However, Santiago (the boy) has a dream, and while he first believes that the dream involves discovering treasure at the Pyramids, he is willing to listen to the teachings of others, like Melchizedek (the King of Salem) and the alchemist. Santiago is able to realize that his happiness does not depend on material wealth. It is only because he is so open to the universe that the universe is able to speak to him and guide him to be much more than he had ever imagined. He is able to speak the universal language, be one with nature and the Soul of the World, and ultimately witness that it is all a part of the Soul of God. Santiago also realizes that love is the greatest treasure in the world. The alchemist knows that the Englishman could never do these things.
The Englishman could ever appreciate the natural world or be humbled enough to believe that something as simple as nature could guide him—and the alchemist knows this. The Englishman has tunnel vision, and without true "vision," he will never swerve from the path he has decided to follow, therefore, we can assume he will never be happy.