<p>&#160;waterfall. The challenge with waterfall is that for complex systems the difficulty increases exponentially.</p> <p>1) might not be able to visualize the end because the end is so different than what they have today</p> <p>2) If they can visualize the end, there may be many many partially implemented paths to get there. Waterfall completely ignores those.</p> <p>3) Business objectives might change over the course of a long project.</p> <p>4) People get burned out just analyzing things without producing any benefit.</p>