Stare decisis is important because it is essential to the doctrine of precedent, according to Cornell University Law School. Stare decisis means a court will stand by a ruling previously issued in earlier cases. This method is used to determine rulings in lower courts as well. Once a court has issued a ruling, all lower courts must have the same response in future cases.
Stare decisis, which comes from the Latin phrase meaning "to stand by things decided," first arose in importance in the 1800s when court cases became more easily accessible to lower courts, lawyers and judges, making it easier for courts to reference previous cases to help inform current ones. As Wikipedia explains, stare decisis sets an interpretation of the law that is expected to be followed in subsequent cases. In the United States, courts seek to follow precedent whenever possible so as to avoid disturbing matters that have already been settled.
Precedents are very rarely overturned, according to The Free Dictionary. When this does occur, it is usually a sign of change in the interpretation of the law. For instance, the landmark case Brown v. The Board of Education overturned a precedent that had been set years earlier by Plessy v. Ferguson. In this case, the courts ignored the precedents already set and ruled racial segregation illegal.
In the United States, stare decisis has been influential in a number of controversial cases. Roe v. Wade in 1973 defined a woman's constitutional right to choose to have an abortion, thereby setting a precedent that has been followed in the majority of related cases tried subsequently, even despite the controversy it has created.