[Thus a useful lesson is learned: always listen to Sebastian, because he's always right.]
--Is impossible, yes? And yet, would any rational explanation fit this situation?
There is precious little reason for you to trust my word, of course. Plenty of people here have magic abilities, and many of them will be happy to demonstrate it to you. Unfortunately, I myself can give no such demonstration.
[Carefully phrasing it like that rather than "I don't have magic powers".]