A broken mirror signals seven years of bad luck. Don't walk under a ladder. Beware of a black cat crossing your path. Don't whistle in a graveyard. Superstitions are everywhere; most of their origins lost in the mists of time.
Theatrical people have many superstitions. "Break a leg" is what you say instead of "good luck". Never whistle or clap backstage. A bad dress rehearsal means a good opening night. Never (and I mean never) quote a line from Macbeth (always referred to as either The Scottish Play or The Scottish Tragedy) backstage. If you do, you have to go outside the theatre, turn around three times, and swear. The whole play is viewed with superstition. I have heard story after story about disasters occurring when Macbeth is performed. Sets fall down. People get injured. Believe it or not, but there's something about that play that seems to invite ill-luck.
Writers have superstitions too. Emma Thompson will only use one specific pen when she writes the first draft of her screenplays. Some won't write "The End" until all the editing, etc. is done. Many writers won't talk about their manuscript until that first draft is completed.
Back when I debated, I always wore a certain shirt and a certain pair of socks to every competition. Other people carried good luck charms in their pockets. It was silly, of course, all of us had done the necessary preparation and were good at public speaking and thinking on our feet, but I would never have gone into a tournament without those socks.
Do you have superstitions? Do you care if you spill the salt; or do you have to throw some of it over your shoulder? Is Friday the 13th just another day? Or would you tear the house apart looking for your special pen? It's almost Halloween; let's air our personal superstitions!