In Paulo Coelho's The Alchemist, why would the alchemist set up such a test (turning himself into the wind) for Santiago?

In 's
, the alchemist and the boy are captured by one of the desert tribes that
is at war. The alchemist gives the boy's gold to the chief and then tells the man that Santiago
is an alchemist and is so powerful that he can turn himself into the wind and destroy them all.
The chief is curious and demands to see if Santiago can do so. The alchemist notes that the boy
must have three days to preparethat he will only turn himself into the wind to show them what he
is capable of doing. Santiago is very much afraid, knowing he cannot become
the wind.

This is why the alchemist puts Santiago in such a terrifying
situation. The boy is learning the ways of the desert and the Universal Language, and feels that
he is approaching his Personal Legend. However, up until this point in the story, it has been
greatly academicSantiago has been able to reason his way between the
different phases that he must pass through in order to realize his Personal Legend, but he has
never been required to put what he knows into practicewhich would change
the way Santiago looks at himself, the world, and his place in the
world.

"Don't give into your fears,"
said the alchemist, in a strangely gentle voice. "If you do, you won't be able to talk to
your heart."

"But I have no idea how to turn myself into the
wind."

"If a person is living out his Personal Legend, he knows
everything he needs to know. There is only one thing that makes a dream impossible to achieve:
the fear of failure."

The alchemist "pushes the
envelope" by putting Santiago into a situation where he must do
all that he is capable of (especially things he
believes he is not capable of) in order to realize his own
potential.

It is for this reason that the alchemist puts Santiago to this
test: so Santiago can realize what he is truly capable of
achieving.