Jim is a new Manager assigned to a Program. He has been briefed by the management about his role, and expectations on the Goal to be reached.
Jim discusses with the team and other stakeholders, makes an assessment of the state of the program and defines a plan to get to the goal post. The plan is reviewed, everyone agrees and the program continues.
As the planned completion date nears, there is a realization that the actual’s are still far far away. why does this happen?
In LEAN thinking we use the terms Current & Future State, look at the image below

In Spite of Jim making an Objective assessment during planning, Cognitive Biases and VUCA forces, result in gap between Current State and Reality.
This hidden gap will always exist, in spite of all the efforts to be close to reality. During planning, It is required to be aware of this Hidden Gap, and plan contingencies for associated Unknown Risks.