Superstition is a belief based on a very poor understanding of the reality that a person or group of people exist in. It can be part of a cultural tradition passed from one generation to the next. It can dictate behavior that can be destructive to societies or to individuals. It can also show the ways that people's brains function when producing consciousness and behavior. When people strive to survive and reproduce, usually any time they think that some behavior or action gives them an advantage, or take away a disadvantage, to them in the environment, they will, if they can, and want to, add this action to their behavior and teach it to their children. If this behavior coincidentally happens at the same time as positive things, it becomes reinforced, even if there is no connection at all to the positive events that occurred.
When it comes to tradition, or their lives, many people do not want change. So even if there is evidence that a superstition is not true it can be perpetuated so as to avoid change.