Throwing salt over your shoulder is considered a superstitious act meant to bring good luck or ward off evil spirits. The origin of this belief varies, but here are a couple of explanations:

1. Christian Influence: One theory connects this practice to a Bible story involving Lot’s wife turning into a pillar of salt (Genesis 19:26). When accidentally spilling salt, throwing a pinch over your left shoulder is thought to blind the devil, who Christians believe lurks behind one’s left shoulder. The act is viewed as a symbolic gesture to counteract the bad luck that spilling salt is often associated with.
2. Ancient Beliefs: Another explanation roots in ancient Roman and earlier beliefs that salt was a valuable and sacred substance. Spilling salt was considered an unlucky omen because of its importance for preserving food and as a symbol of hospitality. Throwing a bit of the spilled salt over the shoulder was a way to propitiate the gods or spirits and reverse the misfortune.
3. Protective Measures: Salt has long been used in rituals for protection and purification in various cultures. Throwing salt over the shoulder might be seen as a way to create a barrier between oneself and evil influences.

While these explanations are not scientifically proven, the tradition of throwing salt over the shoulder persists in many cultures as a harmless and often playful response to spilled salt.