I am totally superstitious. I knock on wood, cross my fingers, step over cracks on the sidewalk, and wish my thespian friends good luck by hoping they break a leg. By the same rule, I avoid black cats, leaving my hat on the bed, or passing the salt from hand to hand at the table.
Many of these bad luck omens are buried in ancient customs, and most of them make sense to avoid: walking under ladders, pouring wine backhanded, opening an umbrella indoors. The worst luck of all is breaking a mirror—not only is it bad luck, it forebodes seven years of misery.