Spilling salt brings bad luck. It is one of those very common superstitions that we learn about when we’re kids and then propagate it once our next generation comes along. There are a few known origins of this superstition, and two of those origins are famous.
The first origin comes from centuries ago. It was a time when salt used to be very costly. It was more valuable than other spices available at that time. So spilling even a little bit of salt was a big wastage of money. Wasting money was considered very bad luck in that period of time because it portrayed that you don’t respect what you have and you were tempting fate; you could end up losing every belonging you had, for this.
The second origin is based on mythology. It is said that if salt is spilled by someone then that person is inviting demons into this world. That demon will haunt the person who spilled the salt forever. To get rid of this fate he/she has to throw some salt behind his/her shoulder. This superstition has been going on for years in the British culture and it isn’t going to go away anytime soon.
Whichever be the origin that you believe in, this is something that many people take seriously. So, if you are a skeptic and while having dinner with someone else you spill some salt then just follow the rules and throw some salt behind your shoulder.
As is the case with most other superstitions, there are many iterations of this also, and depending on whom you ask you’ll get different answers.