26. Common Cause versus Special Cause Insulation
The last several chapters have covered different ways of insulating tasks, resources, individual projects, and multi-projects from risk and variability. These risks and variabilities have been common causes. Common cause variation is those hiccups that occur often in projects, should be expected, and the project methodology should be able to accommodate that variation without management lifting a finger. These variations are primarily internal to the project and account for 80–90% of the variability we expect to observe during project execution. Examples are:
A task taking twice as long to complete as estimated
Some additional tasks being needed to complete the project
A stakeholder ...