Suppose you get sued by a patent troll. You then learn that the troll has been sitting on its patent for years without giving you any warning. If you’d known about the risk, you might have been able to design your product differently to avoid infringement. Even worse, when you try to prove that the patent covers an obvious invention, all of the best evidence (such as websites or code repositories) has disappeared because of the passage of time. Instead of winning the case, you must pay years worth of damages to the troll.