In previous chapters we have considered situations where there was uncertainty about the result that would flow from a decision because any decision could lead to a range of possible outcomes and we cannot be sure which one will arise. There are other occasions where the course of action is already determined but the risks lie in the project not going according to plan. This is a very common situation and one that could, if the deviations from plan are serious enough, lead to some tough decisions that the project manager might be forced to take. Typical examples of deviations from plan are:

Planned activities may take longer than estimated.

Failures may occur on test.

Resources may not be available when needed.

Costs may rise above the amount in the budget.

The external environment might change.

Effects such as these can and will combine to cause the outcome of the project to be different from that in the plan and, for the most part, they will make the position of the project worse. If it is known that some of these effects are likely to happen they can be allowed for in the plan by adding suitable time and cost contingencies. The question becomes one of how much contingency to add and what faith can be had in the result.