Is there insufficient evidence to support the jury's finding that the Gate System's design was not a substantial factor in causing Samuel's injuries?

Samuel argues there was insufficient evidence to support the jury's findings that (1) the "Gate System's design" was not a substantial factor in causing Samuel's injuries, and (2) Builders did not "fail to adequately warn of the potential risks." On issues where Samuel had the burden of proof, we must affirm unless it would be impossible for any rational fact finder to reject his showing. (Blank v. Coffin (1942) 20 Cal.2d 457, 461-462 [126 P.2d 868] [jury's failure to find fact is erroneous only if "evidence contrary to the existence of the fact is clear, positive, uncontradicted, and of such a nature that it cannot rationally be disbelieved"]; Byrum v. Brand (1990) 219 Cal.App.3d 926, 946-947; Horn v. Oh (1983) 147 Cal.App.3d 1094, 1099.)