I very kindly prefer to think that people who don't believe in ghosts have never lived in a haunted house.
I lived in one for a couple of years. It was about 200 years old, so the house had every right to have picked up a spirit or two! I watched as the pull cord on our blinds started dancing as though someone was pulling on them. Pulling and letting go. Pulling and letting go. Over and over and over again. No vents or anything near it, and a vent wouldn't explain how the thing stretched tight then let go. . .
Once I watched in amazement as a dryer door swung out of the way of my head then swung back into place once I was out of the way (we had a stackable washer dryer in our downstairs bathroom).
Our dogs were allowed into the house once when it started raining and we weren't home.
It only got a little creepy when I started taking showers and when I washed my hair I would hear a hard knock in the shower stall. I thought it was the taps, but it was a little creepy so I started varying my routine. The rap always, no matter what I did, occurred when my eyes were closed and I was washing the shampoo out of my hair. Not before. Not after. No washing hair, no rap. I could shampoo then wash off or I could wash off then shampoo. It was always when I was rinsing the shampoo off.
The really creepy moment came when I got out of bed one frosty morning, pulled on my robe and went downstairs. I let the dogs out to do their morning necessities, then I went to do my morning necessities. As I sat down on the throne, my robe fell open and I looked to see two very dark handprints on my calves, positioned with the fingers pointing towards my torso. Fascinated, I put my hands against the handprints. They did not fit. The palms and the fingers were about my size but variant (I believe the palms were larger and the fingers smaller.) My DH's hands are much larger than mine, and we were the only living humans in the house.
A few other smaller things happened, but those are the big ones that convinced me that something was happening in the house. What, I do not know.
I call it a haunting because that is the easiest way to describe it. All I know is what happened.