I have always maintained that ghosts do not exist.
Then I saw one! Must have been seeing things.
Then I saw another! Hmmm, this is getting silly, and worrying.
Then I saw a third, at work. I woman in a maids dress falling from the top of a 7 floor stair well in a big Victorian building. Afterwards, with some research, I found that a maid had jumped, or was pushed, from the top landing after she found herself pregnant following an affair with a Gentleman.
I am stumped. I still maintain that I don't believe in ghosts and that it must be something else imagined or perceived. I just can't explain what I 'know' I saw.