A Novel's Food For Thought By Jack McDevitt in his books Polaris, Echo, and Firebird
Most of us deny the existence of ghosts. There is no spectre abroad in the night, we say. No phantom, no presence lingering over the dying fire, no banshee loose in moonlit trees. No spirit eyes peer at us from the dark windows of abandoned houses. But we're wrong. It's all true. And even though we understand that they are the creations of the mind, they are no less real.
I arrived at last on the street where once I'd lived, and found it full of ghosts.
It is a natural reaction, when a shadow comes at us out of the darkness, a thing we do not know and cannot grasp, to run. And if we cannot run, we will kill it, if we can. Nothing is more certain. Nor should it be.
Ghosts exist. The terrifying aspect of the phenomenon, however, is not that they haunt abandoned houses and dark forests and old cathedrals. No. It is nothing as simple as that. It is rather that they haunt the mind. And, unfortunately, it takes far more than a few prayers or a dash of holy water to get rid of them.
There are such things as ghosts, Henry. Your mistake is that you assume they are inevitably the spirits of people who have died. But many things leave a presence when they have ceased to exist: a childhood home, a lost jacket, a school that has been torn down to make a parking lot. Go back to the street where the home existed, visit the parking lot on a quiet afternoon, stop by the field where you removed the jacket and laid it on the ground while you played ball, and you will feel their presence as you never did in the mundane world.