In many cultures, it is considered unlucky to spill salt. Fortunately, many cultures also have a solution to the problem, which usually involves throwing a pinch of salt over your shoulder. It may seem confusing to modern humans, but knowing that salt was once incredibly valuable can change this perspective.
For thousands of years, salt was an extremely rare commodity. It was difficult to obtain so that the price was very high. Many trading routes were set up to carry salt, people were paid in salt, and salt was sometimes worth more than its weight in gold. Therefore, spilling salt was considered wasteful.
Because of its high value, salt was also associated with friendship and good fortune. Offerings of salt were included in many religious ceremonies, and people might bring salt to a new home for good luck. These associations would have suggested that it would be bad luck to spill salt, since it would seem to violate salt's fortunate properties.
Salt is also an excellent preservative. It prevents food from going bad. As such, it came to be linked with health and longevity. In some cultures, spilling salt was thought to reduce one's well-being. In Britain, for example, each spilled grain was said to represent a tear, while in Germany spilled salt awakened the devil, bringing misfortune.
The fear of spilling salt was also adopted into the Christian faith. It is said that Judas spilled salt at the Last Supper, and since he later turned out to be the betrayer of Christ, spilled salt is considered unlucky by many Christians.
Should you be unfortunate enough to spill salt, you might throw a pinch over your left shoulder to blind the Devil.