The only way to be truly happy in life is to pursue one’s personal legend
I am going to sum up this theme for you. Basically it is saying you will live in regret if you do not pursue your personal legend. This was one of the decsions that Santiago maded during his journey. He had to decide, to either to pursue his personal legend, or stay with his love, Fatima. The Alchemist explained what would happen with each one. If he married Fatima "You'll be the counselor of the oasis. You have enough gold to buy many sheep and many camels. You'll marry Fatima, and you'll both be happy for a year. You'll learn to love the desert, and you'll get to know everyone of the fifty thousand palms. You'll watch them as they grow. Sometime during the seocond year, you'll remember about the treasure. During the third year, you'll still think about your personal legend. You'll spend the rest of the days regreting that you did not pursue your personal legend." If he does go, Fatima will wait for him to come back after he pursues your personal legend, and he will be happy that you did it, but be sad that he left Fatima, and hoping that he will hopefully get to see her again soon. Pursuing one's personal legend, is the only way to be truly happy, that you followed your dream.