What’s a small, harmless superstition or belief that you have?

The absolute first non-food thing I ever bought in China was a jade "bi" pendant. This is what they look like:

(To be clear, this is not mine for reasons which will become obvious in a moment.)

I was told by the seller that you should never take it off as she strung it on red silk for me, because it's to "protect your health".

Since 2001 I've taken this off only five times, all but one of which was because the string frayed through and it had to be restrung. I don't believe in the slightest that it has any impact on my health, but as a minor, neurotic superstition it stays on. (Which is why I couldn't share a photograph of mine: I'd have to take it off.)