From an article by Chinese Culture expert, Jim (Jun) Shan:

There are many ghosts in Chinese culture. Ghosts have been believed and worshipped by Chinese for a few thousand years. Even Confucius said, "Respect ghosts and gods, but be away from them."

Many Asian people believe in ghosts, yet many don't. Chinese people often say, "If you believe it, there will be, but if you don't, there will not." Here is a story about this saying.

Zhuxi was a famous scholar in the Song Dynasty (960 - 1279). He believed there were no ghosts in the world, so he decided to write an essay "No Ghost." It was said he was a great sage, so great even ghosts were afraid of him. If he said no ghosts, ghosts could no longer exist. When the ghosts knew he was writing the essay, they gathered together to discuss this and decided to send the smartest ghost to entreat him abandon the writing.

So one night, the smartest ghost appeared at Zhuxi's desk and kowtowed towards Zhuxi repeatedly. Zhuxi was surprised and asked:

"Where comes the ghost? How dare you disturb me at night?"
"Yes, I am a ghost, but ..."
"Why don't you leave and why do you come in my study room?"
"I am here to entreat ..." replied the ghost.
"People are in the Yang world and ghosts are in the Yin world. We are in the different worlds, so there are no way I can help you."
"I have very important things to entreat you, Sir."
"So, say it!"

Then the ghost told Zhuxi the reason he was there and begged him to abandon the writing to save them. Zhuxi laughed and said:

"You, the ghosts have been worshipped in the human world for so long. Isn't the time for you go away all together?"
"We also have good and bad ghosts..."
"Well, I heard you can do anything. Can you move me to the outside?"
"Certainly, Sir."

Zhuxi was moved to the outside instantly without even noticing it. Zhuxi was astonished by the ability of ghosts, but was unwilling to say it. Then he asked again,

"You can move my body. Can you move my heart?"
"That is impossible to do, Sir. But we can move things or a person's body so that it proves we exist. We exist in the world of illusion. If you believe it, there will be, but if you don't, there will not. Can you say something like that in your essay, Sir?"

Zhuxi felt the words did have some merits so he promised the ghost he would do that. The ghost left happily. Therefore, Zhuxi wrote the words, under the title of the "No Ghost" essay, "If you believe it, there will be, but if you don't, there will not."

So the matter remains undecided even now.