Oh, I didn't believe in ghosts for a very long time. I was terrified of them, but I rationally didn't believe in them.
Then one day I was driving down the interstate and saw a really cute guy in full leathers on a hawg in my rearview mirror. He wore wayfayers and had a nice high and tight hair cut and grin on his face. So I kinda' sorta' watched the road, but I really paid attention to the cute guy behind me on his motorcycle, as I thought to myself "Full Leathers and no helmet? What, you wanna' leave a cute corpse?"
And then. He was NOT there.
Just gone, like someone had flipped a switch. The vehicle I was in (a company rental) filled with the smell of sweaty socks or of sweaty men. (I am completely weird and gross. I ADORE this smell. I know, it's disgusting. I am just wired to love it.

)
There were no exits for miles, no other cars around. I was in the middle of the Cajun prairie on a long, flat piece of Interstate.
A few months later, we had gone to pick up DMIL and bring her to my DM and DF's for Thanksgiving, so I was riding in the backseat of DH's car. We zipped along Autumn country roads, no other cars in sight. At one point, I realized there was a kid, maybe 11, standing a few feet away from the road, watching it. He wore clothes I would more likely assign to the Depression era than today. We stared at one another; the look in his face was just so. Despairing. It shook me to my core.
Blink. No kid. Never had been.
I had a couple of similar encounters; incidents where I was watching someone randomly, and then they just weren't there, times I didn't realize or even think "that is a ghost" until after the switch flipped and they were gone.
But I still didn't believe in ghosts. I don't know what I saw; I called them ghosts for shorthand. I knew we'd seen each other. But I thought there had to be some other metaphysical explanation for it.
Then we moved into a house that was built in the late 18th century. We were told it wasn't haunted. I saw things move, had doors open and close themselves, heard knocks on doors and walls. Still, I was skeptical of ghosts - again, I trusted that something was happening which our modern science had not yet quantified, but was rational. And I was still terrified of the idea of ghosts, even though nothing that happened in the house scared me at all. Not watching blind pulls dance like someone was tugging at them, not having doors open and close to let the dogs in out of the rain, not having a dryer door swing out of the way so that it wouldn't smack me in the face.
Then one morning I woke up with pressure marks on my calves in the shape of hands - hands that didn't match my hands or DH's hands.
And I was totally, completely, utterly, unscared. Not unimpressed. Just Not Scared.

I decided that this was what was meant by haunting, so these must be ghosts, which allowed me to (FINALLY) admit that I've seen a few ghosts in my life. At that point, I stopped being terrified of the idea of ghosts and became completely "meh" about it.
And honestly, I think maybe the ability to see ghosts or sense them or whatever is just something like having a musical ability or mathmatical abilities. It's not anything weird or special, it's just, you know. Some gift you either have or you don't have, and may have just a touch of or have a lot of or have none of.
And I still don't know what ghosts are exactly. I still think that it's just something we haven't figured out how to measure or identify yet, that's all.
And I gotta ask myself why I couldn't have this in spades and set myself up as psychic, instead of having just enough of it to tell true stories at Halloween!