I do not believe in the supernatural, magic, ghosts or anything like that. However, I can be very superstitious about tempting fate and won't make jokes or flippant remarks that could be interpretted as such.

For example, my partner made a dark joke about how she'd rather have cancer than such and such. I begged her not to say such things, not because the thought of her having cancer upset me (although it did), but because it feels as if saying stuff like that could make it happen.