Superstitions began centuries ago when our ancestors tried to
explain mysterious circumstances or events as best as they could
with the knowledge they had.
For instance, before the development of science explained such
strange things as why mirrors show our reflections or why shadows
appear when it's sunny, ancient people reasoned that a shadow or
reflection was part of their soul.
If someone broke something onto which the shadow or reflection
appeared, people believed that their soul was harmed. Therefore,
when a person broke a mirror it was considered unlucky or
harmful.
Today we know that reflections and shadows are not part of our
souls but if someone still believes it is bad luck to break a
mirror they are said to be superstitious.
So a superstition is a belief or practice that people cling to even
after new knowledge or facts prove that these silly beliefs are
untrue.