In The Alchemist by Paulo Coelho, the gypsy woman begins the cycle of adventures that will ultimately lead to Santiago listening to his heart and fulfilling his dream.

The gypsy woman tells Santiago that she can interpret dreams and that they are the "language of the world." However, she cannot interpret the dreams that are the language of the soul. For each and every individual, one must find a way to listen to his own heart to uncover his personal path.

Santiago begins his adventure as an Andalusian shepherd who has a recurring dream under a sycamore tree that tells him there is great treasure to be found at the pyramids, and he must follow this dream to discover his Personal Legend. When he visits the gypsy, she tells him that he must go as well. Therefore, the gypsy woman becomes the spark that ignites Santiago's personal quest, a quest that each person must undertake if they are to find the true meaning of life. Along the way, he has many adventures, and he is able to realize his dream and understand that life is a spiritual journey.

The gypsy woman merely reiterates that the boy, who dreamed that he went to the Pyramids of Egypt and found a great treasure, must go on his quest.  The reason Santiago went to see her was because he'd had the same dream twice, and he was hoping for a more in-depth explanation.  When she merely reiterated the obvious message of the dream (go to the Pyramids), he at first was discouraged in her so-called abilities (but happy that he didn't have to pay for her services because she'd requested 10% of the treasure if and when he found it..and he did not take the dream seriously at that point).  However, like many ideas, once they have been brought to mind and then confirmed by another, they have a way of growing on a person's imagination.  After speaking with her, the dream seemed to become more real to Santiago, and then his chance meeting with the King of Salem further confirmed that he should go to the Pyramids.  If he had not spoken with the gypsy woman, he might have just ignored the dream and would never have sought out to fulfill his Personal Legend.  Happily, when Santiago eventually does find the treasure, he remembers his promise to the old woman and gives her 10%.