"My mom is up all hours of the night pacing, like she's haunted - a ghost with an unnamed grudge." - Nate Expectations by Tim Federle. Hearing this quote while listening to the audiobook "Nate Expectations", specifically the line "a ghost with an unnamed grudge," made me want to name 10 possible grudges that might cause a ghost to haunt someone.
1. S/he was murdered, and their murderer still roams free.
The most obvious reason for a haunting.
2. They were locked in the attic (or other room) for much of their life.
3. Unrequited or unadmitted love
4. Someone stole something - either a prized possession or significant person, from them.
5. The ghost doesn't realize they are dead.
6. Someone stopped them from following through with their dreams
7. Someone could have saved them from dying but didn't.
8. Someone who cheated against them in a major life event, causing them to lose - like an election, a big game, or major sports event.
9. Someone who was blackmailed or otherwise forced to do something against their will, such as "losing" or discounting election ballots to keep the other from revealing something about them they wanted kept secret.
10. Someone they trusted revealed a secret that they wanted kept hidden, which changed the course of their life.