Superstitions, then and now

Superstitions can be defined by a unjustified belief in an supernatural thing(s) that causes someone to perform certain rituals.

Each superstition has an idea behind it. For example, never going under a ladder, especially if a black cat has walked under it. This has the idea of bad luck; which is what most superstitions are related to. Either good or bad luck and how you obtain one of these two.
In Macbeth you can see the fear which some may say lies within the first scenes where the three Witches in the dark hospital are chanting over a dead body. Really thereafter, the witches are seen in a negative light, people someone would go to if they needed the future to be told to them. But feared because very little is known about them and their abilities are seen as dark, evil, and unholy; perhaps even associating it with the devil.
Throughout the movie Macbeth are shown some of the victims that he murdered, they tell Macbeth their thoughts and feelings about him. Which leads into the point that superstitions can be in the form of seeing the dead.

Today superstitions are based off of stories where either the person in the story suffered a bad or good event because of it. TOday superstitions are still believed and followed so as to avoid bad luck or to encounter good luck.  In both now and the past, most superstitions are things that are usually seen in a negative light. 

http://www.angelfire.com/fl3/Defymcbeth/Super2.html