Using the scientific method as the theory of knowledge leads to selecting the preferred theory through critical discussion and test. Comparing critical chain to critical path, we see more content in the critical-chain theory because it
1. Provides an explicit method to manage common-cause variation;
Popper  notes that a new theory should contain and explain the old. With unlimited resources, the critical chain is the same path as the critical path. With a resource constraint, the critical chain is an acceptable solution to the resource-leveled critical path. Thus, the critical chain contains the critical-path solution.
Popper suggests that the primary method of testing a new theory should be through critical discussion. This discussion checks the new theory against the old, looking for logical deductive reasoning and evidence supporting the suppositions (assumptions) made in the new and the old theory. Summarizing the reality of the scientific method, Popper states,
1. Induction (i.e., inference based on many observations) is a myth. It is neither a psychological fact, nor a fact of ordinary life, nor one of scientific procedure.
2. The actual procedure of science is to operate with conjectures: to jump to conclusions—often after one single observation.
3. Repeated observations and experiments function in science as tests of our conjectures or hypotheses (i.e., as attempted refutation).
This chapter has developed the reasoning behind the way Goldratt defined the problem with the current theory. It does not explain the jump to his proposed direction for the solution: improved management of uncertainty. It is unlikely that others without his knowledge and experience could have made the same jump. The original PERT method and subsequent work with project simulations provide evidence that others were aware of the uncertainty problem.
The current knowledge base lumps the uncertainty in predicting each project task in the area of risk management, adding evidence that people understand the need to deal with variation. However, none of the current solutions makes uncertainty management part of the basic project system in the manner of the critical-chain method. My approach to CCPM clarifies that buffers serve to manage common-cause variation, while conventional deterministic risk analysis and management handles potential special-cause variation and uncertainty. This is one way CCPM brings the power of Six Sigma and TQM to critical chain.
Critical chain explains the reasons for schedule overrun through the reality of statistical fluctuations (uncertainty or variation) and dependent events. The CPM theory does not address this reality; it uses deterministic durations, start dates, and stop dates for activities in the schedule. Combining this technical assumption with human behavior leads to schedule overrun. Schedule overrun leads to cost overrun and reduces the delivered scope. Perhaps most importantly, the new theory explains how the CPM theory, through the win-lose approach to task scheduling, causes much of the psychological harm in project systems.
The resource constraint is every bit as real as the task-input constraint. It is a necessary condition to perform the task. The CPM assumes that an acceptable solution to the resource constraint is first to find the unrestrained critical path and then to assess the impact of the resource constraint. Put another way, determination of the critical path assumes that resources are not the constraint. Alternatively, it assumes infinite resources. I could find no references describing the reasoning behind this assumption. Goldratt found it easy to notice this implicit assumption because it was made as an explicit assumption in the production system models he had worked with .
Some users of CCPM have asserted that the resource constraint need not be "as real" as the technical constraint. In other words, for many pieces of work, you simply cannot change the task sequence: you have to put in the foundation before you place the equipment, or you have to remove the equipment before you can reinstall it. However, often one can put resources on overtime, including extended workweeks, or elevate the resource through a variety of approaches. This does not conflict with CCPM because the plan maintains the technical sequence of tasks. All tasks require both the technical predecessor and the resource to work. CCPM does not preclude using alternatives to elevate the constraint.
This chapter has demonstrated that the CPM usually fails to identify the real constraint to the project (resources). It is a simple and logical step to define the critical chain as the combination of the two potential constraints on the longest path to complete the project.
Chapter 1 presented selected successful evidence that the critical-chain method creates the DEs. (It is selected in the sense that it is not an exhaustive listing; this does not mean we selected only the positive results!) By this time, thousands of projects of different types, in different businesses, and in different cultures around the world, have successfully applied critical chain. However, there are cases where implementation failed to achieve the changes necessary for critical chain, and the project system continued to operate the old way. Chapter 9 addresses this in detail.
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What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.