What is the secret?

"Goodbye," said the fox. "And now here is my secret, a very simple secret: It is only with the heart that one can see rightly; what is essential is invisible to the eye."

...

He was tired. He sat down. I sat down beside him. And, after a little silence, he spoke again: "The stars are beautiful, because of a flower that cannot be seen."

I replied, "Yes, that is so." And, without saying anything more, I looked across the ridges of sand that were stretched out before us in the moonlight. "The desert is beautiful," the little prince added.

And that was true. I have always loved the desert. One sits down on a desert sand dune, sees nothing, hears nothing. Yet through the silence something throbs, and gleams...

"What makes the desert beautiful," said the little prince, "is that somewhere it hides a well..."

I was astonished by a sudden understanding of that mysterious radiation of the sands. When I was a little boy I lived in an old house, and legend told us that a treasure was buried there. To be sure, no one had ever known how to find it; perhaps no one had ever even looked for it. But it cast an enchantment over that house. My home was hiding a secret in the depths of its heart...

"Yes," I said to the little prince. "The house, the stars, the desert - what gives them their beauty is something that is invisible!"

"I am glad," he said, "that you agree with my fox."