I have heard some daft ideas in my time, but there was one which I came across years and years ago which has stuck in my mind ever since I first heard it. It wasn’t so much an idea, as a theory of life and I think it is also used to show the importance of logic in an argument.
The theory states that I am the only person in the world. No one else exists, just me. That is when the argument starts, because you chip in with the comment that you are there too, so I am wrong. Ah, but you are only there as part of my imagination. I am making you say that you are there.