Absent an attorney affidavit of fault, a motion made pursuant to Code of Civil Procedure section 473, subdivision (b) is discretionary. That means it is not mandatory for a trial judge to grant such a motion, and on appeal you would have to show an abuse of discretion, which is the worst appellate standard, because the Court of Appeal will defer to the trial court.
Any mistake of law, even though made by a self represented party, is not excusable neglect. (Anderson v. Sherman (1981) 125 Cal.App.3d 228, 237-238.)
