h commercial and artistic endeavors is fostered by a rule of law that gives people confidence about the legal consequences of their actions. FN18. See General Motors Corp.'. Romeln, 503 U.S. 181, 191, 112 S.Ct. 1105, 1112, 117 L.Ed.2d 328 (1992) ("Retroactive legislation presents problems of unfairness that are more se