Good Luck

I'm not superstitious. At all. Just because I can't explain something at a given moment, I don't think ascribing its cause to some bit of cultural voodoo is particularly rational.
Take walking under ladders- it will bring you bad luck. I do not walk under ladders. Why? Because it may fall on me.
A black cat crossing your path may bring bad luck. Well, if you're driving & have to brake suddenly, then someone may rear-end your car.
It seems to me that people are confusing superstition with basic Health & Safety advice.