阅读下面材料，从选项中选出最佳选项。
A businessman's son wanted to learn the secret of happiness from the wisest man. The boy walked through the desert for forty days until he reached a beautiful castle at the top of a mountain where the wise man lived.
When he entered a room, the boy was so surprised: businessmen coming and going, people chatting in the corners, a small band playing sweet music, and all kinds of delicious dishes on a large table.
The wise man talked with everyone. The boy had to wait for two hours until it was his turn.
With enough patience, the wise man listened to the reason for the boy's visit, but he was too busy to explain to him the secret of happiness. He suggested that the boy take a walk around his palace and come back in two hours.
“However,"he added, handing the boy a teaspoon with two drops of oil in it, “while you walk, carry this spoon and don't let the oil go out.”
The boy thought he must follow what the old man had said, so he always kept his eyes fixed on the spoon while walking. At last he returned to the wise man.
“So,”asked the wise man,“did you see the famous paintings in the hall? Did you see the garden that took the master gardener ten years to create?” Embarrassed, the boy said that he had noticed nothing. All his attention was on the spoon.
“OK. Now go back and see the wonders of my world,” said the man. Now more relaxed, the boy took the spoon and walked again through the palace. After his return, he exactly reported all that he had seen.
“But where is the oil?”asked the wise man. Looking down at the spoon, the boy realized that he had spilled (溅) it all.
“Well, the secret of happiness lies in ___________________.”the wise man said with a smile. Then the boy realized what happiness was.