When you design a hammer and sell it to the end user, there are limitations on how they can use it. You simply cannot encompass and address every situation that

When you design a hammer and sell it to the end user, there are limitations on how they can use it. You simply cannot encompass and address every situation that the end user would subject the hammer to. What if they left the hammer in a hot 1500 C oven? The designer cannot design it such that it can universally work in every situation. There are usage guidelines and limitations. A hammer that melts in a furnace is considered a bug? The possibilities and test paths a piece of code can possibly take exceeds a very large number in a complex software application.