When you are coding in a hurry, it is very tempting to write business logic in the first place that comes to mind, such as a button click handler in your UI code.  However, for all but the simplest systems, such a practice leads very quickly to a system that is very difficult to work with, much less modify, because its business logic is scattered like the ash from an erupting volcano.  So let's take a step back and see how you can develop an application more intelligently.