What is the behaviour of the curve during different time intervals, such as at (0), (0, 20-30%], (20-30%, 50%], (50%, 75%], and (75%, 100].
Brief analysis and points of discussion:
Since a project has a temporary endeavor, the timeframe has to be finite. The broken lines in the graph represent finite areas such as phases or milestones. The black graph represents the estimated project plan schedule, the blue graph represents an early schedule, and the red graph represents a lagging schedule.
In an ideal situation the beginning is usually slow because people need to acquire confidence with the project, and once the schedule has achieved 20-30% of the work completed, the slope of the graph will change and will accelerate due to the confidence and knowledge acquired. At 70-80% the schedule has reached a very good level of control and will continue with confidence to full completion of the project.
What is the scenario before Time=0, i.e., before launching of the project?
In practice, most organizations don't really start from scratch when launching a project. Some pre-analysis work has been done in order to get an idea of what has to be done in terms of requirements, characteristics and resources needed for the project. With this information (although it's at high level), it's possible to make an estimation of the time and cost; decisions are usually taken after this information is available (or at least we reach a confidence level of 80%). The realization of a successful project will require commitments from the operating organization and all stakeholders.