A man is driving down the road and his car breaks down near a
monastery.

He goes to the monastery, knocks on the door and says, "My car broke
down. Do you think I could stay the night:"

The monks graciously accept him, feed him dinner, even fix his car.

As the man tries to fall asleep, he hears a strange sound. A sound not
like anything he has ever heard before.

The Sirens that nearly seduced Odysseus into crashing his ship comes to
his mind.

He doesn't sleep that night. He tosses and turns trying to figure out
what could possibly be making such a seductive sound.

The next morning he asks the Monks what the sound was, but they say,
"We can't tell you. You're not a Monk."

Distraught, the man is forced to leave.

Years later, after never being able to forget that sound, the man goes
back to the monastery and pleads for the answer again.

The Monks reply, "We can't tell you. You're not a Monk."

The man says, "If the only way I can find out what is making that
beautiful sound is to become a Monk, then please, make me a Monk."

The Monks reply, "You must travel the earth and tell us how many blades
of grass there are and the exact number of grains of sand. When you
find these answers you will have become a Monk."

The man sets about his task.

After years of searching he returns as a gray-haired old man and knocks
on the door of the monastery. A Monk answers. He is taken before a
gathering of the Monks.

In my quest to find what makes that beautiful sound, I traveled the
earth and have found what you asked for."

"By design, the world is in a state of perpetual change. Only God
knows what you ask. All a man can know is himself and only then if he
is honest and reflective and willing to strip away self deception."

The Monks reply, "Congratulations. You have become a Monk. We shall
now show you the way to the mystery of the sacred sound."

The Monks lead the man to a wooden door where the head Monk says, "The
sound is beyond that door."

The Monks give him the key and he opens the door.

Behind the wooden door is another door made of stone.

The man is given the key to the stone door and he opens it only to find
a door made of ruby.

And so it went that he needed keys to doors of emerald, pearl and
diamond.

Finally they come to a door made of sold gold. The sound has become
very clear and definite. The Monk says, "This is the last key to the
last door."

The man is apprehensive to no end. His life's wish is behind the door!

With trembling hands, he unlocks the door, turns the knob and slowly
pushes the door open. Falling to his knees he is utterly amazed to
discover the source of the haunting and seductive sound.

Spoiler for The source of the sound: