This is a true relic- the few who can spend the time and read it will be rewarded with the gift of understanding state. Using the complex example of…. a calculator:
At first glance, this approach seems to work just fine. Indeed, when you launch the calculator (available for download at <www.cuj.com/code>), you will certainly find out that most of the time it correctly adds, subtracts, multiplies, and divides. What’s there not to like? However, play with the application for a while longer, and you’ll discover many corner cases in which the calculator provides misleading results, freezes, or crashes altogether.
Source: Who Moved My State? | Dr Dobb’s