Consider building mobile phones on an assembly line: It is possible to unambiguously define the specifications and construction steps. After building some phones and measuring things, it is possible to reliably estimate and schedule the building of future phones.
A different problem: Build a custom house. The owner wants to use new environmentally friendly materials and methods, but isn't exactly sure what they want, and is going to change or clarify their decisions as they see the house, costs, and weeks unfold.
At one end of the spectrum, such as manufacturing phones, there are problems with low degrees of novelty or change, and high rates of repeated identical or near-identical creation mass manufacturing or predictable manufacturing.
At the other end, there are problems with high degrees of novelty, creativity, and change, and no previous identical cases from which to derive estimates or schedules. This is the realm of new product development or inventive projects.
The development process, management values, planning and estimation models appropriately associated with these two domains are different (Table 1.1).
Of course, the point is,
Plus, many projects use new and buggy technologies that exacerbate the degree of novelty and unpredictability. Note also it is a new product for the inexperienced even if it has been done before.
Since predictable manufacturing is the wrong paradigm for software, practices and values rooted in it are not helpful.
Factors [CP86] preventing reliable up-front specifications include:
This deep appreciation that building software is complex, new product development with high change rates, and not predictable manufacturing is at the heart of the motivation for agile and iterative methods.
Certainly, another driving force is the desire to compete and win. Iterative and agile methods foster flexibility and maneuverability a competitive advantage. In Agile Competitors and Virtual Organizations [GNP97] the authors examine the limitations of the mass manufacturing model and the need for agility: