When someone mentions “waterfall has always worked for us”, I believe this is an example of Type Three error. The real question – has waterfall been optimal? The example I always give is that the covered wagon was successful for transportation, but when I look out the window of a plane, I don’t see any crossing the prairie. In the case of those applying the values and principles of agile properly there is little doubt as to which is the airplane and which is the covered wagon.