The superstition that a person will suffer seven years of bad luck if they break a mirror is one of the most widespread superstitions of all time. Prior to the invention of mirrors, myths surrounded the reflections men and women that were seen for example in a lake or pond. The belief emerged that the reflection was a visual representation of the soul which was temporarily “away” from the body. If the water was (and hence the reflection) was disturbed, it was considered to be a bad omen.
When mirrors were invented, the art of scrying (divining information) came into practice. One common practice of scrying was the the seeking out of witches. Some fearful of witchcraft possessed small “witch-balls” made of reflective glass that were said to ward off sorcerers. The superstition grew to include the breaking of mirrors. Many tie the seven years bad luck theory to the Romans who believed that life (the soul) renewed itself every seven years.
Several antidotes have been prescribed to counteract the breaking of a mirror. These include: burying the broken pieces in sacred ground or throwing them into a swift-flowing stream.
Sources: Dictionary of Superstitions, Wikipedia, Snopes
