In Carlisle v. Harp (5th Dist. 1990), 200 Ill. App. 3d 908, 146 Ill. Dec. 355, 558 N.E.2d 318, the defendant's attorney started arguing comparative negligence in his opening statement to the jury. Plaintiff objected on the ground that the plaintiff's comparative negligence was never affirmatively pleaded by the defendant as an affirmative defense and therefore plaintiff's comparative negligence was not properly before the jury. Defendant contended on appeal that the trial court erred in refusing to allow the defendant to amend his answer to allege the plaintiff's comparative negligence after the trial had begun. The Fifth District Appellate Court ruled that the defendant's mistake of failing to allege plaintiff's negligence as an affirmative defense, which was not discovered until trial, does not constitute a good reason for not filing the affirmative defenses with the original pleading.