The doctrine of res judicata

The doctrine of res judicata is a legal fiction. It is founded on the realisation of Roman lawyers of the undeniable truth that no judge can assuredly ascertain the facts correctly, but that for the sake of finality and to avoid the scenario where parties to the same dispute reagitate the issues, even an erroneous decision of a Court ought to be accepted as truth. 

5. For the doctrine of res judicata to apply, the Court should have jurisdiction of the subject matter, the parties to litigation must be the same, the cause of action should be the same, the dispute should have been adjudicated on its merits, etc.