The (false) belief that large, innovative software designs can be completely specified in advance and then painlessly magicked out of the void by the normal efforts of a team of normally talented programmers. In fact, experience has shown repeatedly that good designs arise only from evolutionary, exploratory interaction between one (or at most a small handful of) exceptionally able designer(s) and an active user population — and that the first try at a big new idea is always wrong. Unfortunately, because these truths don't fit the planning models beloved of management, they are generally ignored.