The gyspy woman that Santiago goes to in order to find out the truth of his dreams is very open with Santiago that the interpretation of his dream is very difficult, which is why she feels she is able to make a demand for a tenth of the treasure that he will find if he follows his dreams. She goes on to elaborate why it is that his dream is so difficult to interpret:
I told you that your dream was a difficult one. It's the simple things in life that are the most extraordinary; only wise men are able to understand them. And since I am not wise, I have had to learn other arts, such as the reading of palms.
The dream is therefore difficult to interpret because it is based around "the simple things in life." Santiago's dream is related so closely to his own Personal Legend and the simple desire to grow and develop as a human being, and this is what makes his dream a challenge to interpret. It can also be argued that the effort that the gypsy woman puts into the interpretation of the dream foreshadows the effort that Santiago will need to put in for him to achieve his Personal Legend. Nothing that is worthwhile comes easily without personal cost, as Santiago discovers. Note to that this section of the novel develops the motif of dreams as being a form of communication with the Soul of the World. It is this initial dream, after all, that sets the entire plot in motion as Santiago embarks on his quest.
thank you this is very important! :)