Roscoe had one more point he wanted to make. Once again, he reached for the napkin holder and pulled out a fresh "canvas" for his final sketch.
"No doubt you have seen curves like this that contrast waterfall development with iterative development," he said, as he sketched Figure 5.3.
Figure 5.3. Roscoe's third drawingwaterfall versus iterative.
"The basic message here is that waterfall development remains high risk for much longer, because until there is meaningful system integration, we don't really know where we stand. With iterative development, which employs risk targeting and meaningful integration-and-build activity from the first iteration, risk is squeezed out early. In both pictures, point 'D' represents the decision point at which we might decide to cancel the project. That is, if the risk curve does not begin to plummet at that point in time, we might decide that we can't go on; without a diminution in project risk, maybe we cannot and should not continue to invest."
"Sure, Roscoe," I said, "I've seen Dave Bernstein draw those curves for years. No news there. Clearly, it is better to make this decision early rather than late. So waterfall is the inferior approach."
"Yeah," countered Roscoe, "but there is a second, less well-understood reason that makes iterative development even more compelling. And I'm going to show it to you right now."