Superstitious beliefs are often a byproduct of predictable errors we make in processing our world. We're trying to find explanations for things that are pretty commonplace. Most people, once they have developed a belief, tend to look for experiences that support the belief but do not acknowledge experiences that run contrary to that belief. What we notice are confirmed instances of our beliefs and ignore what would challenge our beliefs. For example, people often consider the thirteenth day of the month to be unlucky, especially if it falls on a Friday.
Superstitions also extend into the religious realm.
According to David Crump, professor of religion and theology, superstitions are evident throughout the Bible, even in miracles performed by Jesus himself. When Jesus healed a blind man, he spit on the mud used to heal the man's eyes. The power of a person's soul, Crump said, was contained in the saliva. This superstition is practiced even today when boxers spit on their hands before a match for good luck. They may not realize the origin of their actions, but they may feel some sort of confidence from the ritual.