In Coelho's The Alchemist, what does Melchizedek consider to be "the world's great lie?

In the
novel , much of the story revolves around a theme of fate and
predestination. Santiago believes for a vast majority of the tale that he is being guided by
fate and that he can do nothing to change his future. He believes in the constraints of fate, in
short.

However, Melchizedek, the ancient king of Salem and precursor to the
Jewish Kings and Christ himself, appears to him to counsel him otherwise. He tells Santiago that
the greatest lie in life is that we are controlled by fate and that we lose our free will. When
we become convinced of this, we lose the power in our life and stop striving to reach our goals
and succeed. This advice motivates the young man to continue on his journey.