Extreme Programming: A Gentle Introduction. A simple design always takes less time to finish than a complex one. So always do the simplest thing that could possibly work. If you find something that is complex replace it with something simple. It's always faster and cheaper to replace complex code now, before you waste a lot more time on it. Keep things as simple as possible as long as possible by never adding functionality before it is scheduled. Beware though, keeping a design simple is hard work.