How to understand it
Any plan is a statement of what is expected to happen, although as many planners will agree, the best laid plans of mice and men seldom happen exactly as expected. There are two approaches to coping with this problem: firefighting or risk management.
Firefighting is an approach that is taken surprisingly often. The manager spends most of his or her time coping with the unexpected, issuing orders, changing plans and slipping schedules. It can give a false sense of heroism as immediate dangers are averted by dramatic last-minute actions.
On the other hand, risk management involves looking ahead at the planning stage for potential future problems. The most difficult part of this activity is often the actual identification of risks. The Process Decision Program Chart (commonly abbreviated to the less unwieldy PDPC) provides a simple method to help in identifying both risks and countermeasures.
Quite simply, if the plan is displayed diagrammatically (typically in a Tree Diagram), then identified risks and countermeasures are added in subsequent boxes, as Fig. 1. below. This may appear to be quite trivial, but as with many other tools, the construction and thought involved is as important as the final diagram.