It is often said that litigants only get one kick at the can and cannot try again later with a better pair of boots. The doctrine of functus officio operates to effectively impose the same restraint on judges.
As a general rule, once a judge has rendered a final decision, she is barred from reopening, varying or retracting her decision. She cannot do so because, having pronounced judgment – provided that there is no reservation of any kind in the judgment – the judge is said to be functus officio (Latin for “having performed one’s office”) and is divested of jurisdiction over the matter. If the decision is wrong or otherwise unsatisfactory, the recourse is for the aggrieved party to appeal it.
Functus Officio: No Second Kick at the Can for Judges
Toronto Law Journal, May 2018