What is the test for impeaching a jury verdict in a long-delayed jury trial?

[650 P.2d 1190] We take this opportunity to emphasize our unwillingness to allow the impeachment of jury verdicts on a bare showing that some jurors failed to conform their conduct to the ideal standard of utmost diligence in the performance of their duties. Even the most diligent juror may reach the end of his attention span at some point during a trial and allow his mind to wander temporarily from the matter at hand. We do not condone such conduct and trust that trial courts will be alert and take appropriate action if it occurs. But we recognize that this is especially likely to occur in such a complex and lengthy trial as the case at bar. Retrials are to be avoided unless necessitated by a more substantial dereliction of jurors' duties than was evident in this case. "Society has a manifest interest in avoiding needless retrials: they cause hardship to the litigants, delay the administration of justice, and result in social and economic waste." (Mercer v. Perez (1968) 68 Cal.2d 104, 113, 436 P.2d 315.) This plaintiff was seriously and permanently injured in 1970. He has prevailed in two lengthy jury trials, but for twelve years has received no recovery. Justice will not be served by a second reversal, yet another lengthy trial, to be followed in all likelihood by further appeals.