The alchemist shows the Englishman that his doubt and fear are the only things holding him back.
When the Englishman finds the Alchemist and asks him to teach him alchemy, the Alchemist's simple answer to him is "Go and try". Throughout the long trek across the desert, Santiago sees the Englishman looking for answers in his books. The Englishman tells the boy that he has been studying and reading in hopes of learning alchemy. He's searching for someone to answer his question rather than trying to figure it out on his own. In his simple statement, the Alchemist is allowing him to put aside doubt and fear to attempt the experiments on his own.
