In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Sardines
If you dream that you are eating tinned sardines then you will learn something of benefit to you, but if they are fresh then you will have an argument at home.