All projects are affected by cost, schedule, and technical risks, created by reducible and irreducible uncertainty - Virien and Trumper 2013.
Cost and schedule growth for complex projects are created with unrealistic technical performance expectations, unrealistic cost and schedule estimates, inadequate risk assessments, unanticipated technical issues, and poorly performed and ineffective risk management contributes to project technical and programmatic shortfalls.
Root causes of this cost and schedule growth and technical shortfalls on projects start with not adequately specifying what Done looks like in Measures of Effectiveness for the project's outcomes prior to starting the project, not quantifying the uncertainty and failing to manage the resulting risk for the Measures of Performance associated with the Measures of Effectiveness during the execution of the project.
