What is a ghost? A physical apparition of someone that is gone but still walks the earth among us. They've left us but their sole still lives with us. Why? Maybe they were murdered or have an attachment to an item of some sort. Maybe a house or doll that once belonged to a little girl. Perhaps nothing happened to them in their lives. But someone has defiled their grave and it wants its revenge so it haunts people until it gets its peace.
Whether that's what a ghost is or why it remains with us a ghost has a reputation and lives by it. That reputation comes from its tale. Every ghost has a tale and that tale can be stretched on by generations of story telling.
But what about the ghost how does he feel to be stuck in a time he doesn't belong in. Every person he sees just runs in fear and doesn't even want to do anything with him. After years and centuries of this maybe the ghost snaps and lives up to its reputation as a scary and hurtful individual. Then when his tale is almost lost no one sees him. Only a couple teenagers try to get scared by his presence.
All he can do is lay awake and wait for someone to help him get away from his hell. He tries to remember where it all went wrong and why he is punished to be alone for the rest of his existence. But that's okay because he has the rest of eternity to think about that one.