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. v. &mein, 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 serious th