Myth No. 2: Scrum Wont Work on a Fixed Schedule and Budget
Myth No. 2: Scrum won't work on a fixed schedule and budget
This may be the most common myth one hears when first introducing Scrum concepts. This myth, too, is understandable given the dramatic differences between a Scrum approach to planning and execution and a more traditional approach such as "waterfall." Scrum uses a planning approach called "progressive elaboration" or "rolling wave."
Rolling Wave Planning is "a form of progressive elaboration planning where the work to be accomplished in the near term is planned in detail, while the work far in the future is planned at a relatively high level, but the detailed planning of the work to be performed within another one or two periods in the near future is done as work is being completed during the current period," according to the Project Management Body of Knowledge (PMBOK) Guide, Fourth Edition.
Such an approach is in stark contrast to a traditional approach where we construct an elaborate, up-front plan that contains the details of all the work to be done (we think), and project health and progress is measured by deviation from this baseline plan. This is referred to as a "plan-driven approach."
Scrum is based on a completely different set of assumptions. Scrum assumes, in the words of quality management guru Philip Crosby, "if anything is certain, it is that change is certain. The world we are planning for today will not exist...tomorrow." For the kinds of work where we would consider the Scrum approach (typically, complex creative development work), Scrum recognizes that we cannot reasonably determine all the details of the work up-front and won't have a fuller understanding-no matter how long we think and talk about it-until we start building something. Scrum then replaces a defined process, the plan-driven approach, with an adaptive and evolutionary process that's referred to as a "value-driven approach."