A more thorough explanation:

The "law of the case doctrine" is a legal principle that states that the decision made by an appellate court on a legal issue is binding on both the trial court and the appellate court in any subsequent retrial or appeal involving the same case and substantially the same facts. This means that the appellate court's ruling on the questions presented to it becomes the "law of the case."

The purpose of this doctrine is to promote finality and judicial efficiency by minimizing unnecessary relitigation of legal issues that have already been resolved by the appellate court. If a court has already decided a legal issue in a case, the parties cannot bring up the same issue again in a later proceeding.

For example, if a defendant appeals a conviction and the appellate court rules that the evidence was obtained illegally, the trial court must exclude that evidence in any subsequent retrial. The appellate court's decision on the legality of the evidence becomes the "law of the case."

However, if new facts are presented in a subsequent proceeding that materially affect the legal issues at hand, the court may apply the law to the new facts as they are found.

It is important to note that the law of the case doctrine only applies to issues that were decided "directly or by implication" in a prior decision. It does not apply to issues that were not addressed in the prior decision.

Other related legal principles include res judicata and stare decisis.