Recently at World Politics Review, U.S. Marine Corps’ veteran and defense analyst Jonathan Rue published a lengthy essay on the defense budget fight currently roiling both Congress and the Pentagon. Rue makes a number of important points ranging from the Pentagon’s decision to ignore the existence of the Budget Control Act spending limits instead of planning for them to the defense establishment’s focus on budget inputs to the detriment of assessing national security outputs. It is an excellent essay and worth reading in full, but one point that Rue makes in passing in regard to the Pentagon’s planning system seems worthy of further consideration.

In chiding the Department of Defense for failing to prepare for the Budget Control Act’s spending limits, Rue writes, “The Defense Department’s Planning, Programming, Budgeting and Execution (PPBE) system needs stable, predictable budgets. Sequester-level caps may be too low, but at least they’re predictable.” And he is absolutely right. But because PPBE is not the focus of his essay, Rue does not explore the implications of the system’s need for predictability further.

PPBE is the legacy of Robert McNamara’s Planning, Programming, and Budgeting System (PPBS). In 1961, when McNamara instituted it, PPBS was the state-of-the-art in corporate planning—intended to rationalize the conflict-prone military service-driven planning system that preceded it. Unfortunately, the rational design model on which PPBE is based fell out of favor in the business community decades ago—while McNamara’s system remains largely in place, with only marginal alterations.

The problem with PPBE’s reliance on predictability is twofold. First, as Rue notes, PPBE requires predictable budgets. However, the history of defense spending has been one of ups and downs and the assumption that defense spending is on an upward trajectory locks in bureaucratic preferences that are difficult to change when a downward turn occurs. Budgets are the product of a political process that has shifting priorities. Threats—both in reality and in perception—will vary and other fiscal priorities will take precedence. Sometimes, these shifts will happen with enough lead-time for Pentagon planners to adjust accordingly—as was the case when Congress passed the Budget Control Act and the “supercommittee” failed to find the savings necessary to avoid sequestration. However, in the months prior to the sequester going into effect in March 2013, it is likely the various bureaucracies were busy trying to salvage plans made several years in advance rather than adjusting to the new reality they faced.

The second problem with PPBE’s reliance on predictability is external. It assumes a certain level of predictability in the international environment that will conform to PPBE’s three-stage, multi-year planning process. Both intelligence and various strategic planning documents—such as the Quadrennial Defense Review—play a major role in guiding PPBE’s planning process. These documents rarely present an accurate vision of the world several years in the future. Prediction is difficult and relying on it provides perverse incentives to the military services and defense agencies when the predicted threat environment proves illusory. Just as a lack of predictable budgets likely leads to bureaucracies holding dear to plans laid when the budget was thought to increase, changes in threats will likely lead to new justifications for plans already in place.

PPBE has several attributes that lead it to have a status quo bias. The need for predictability is one of the most important. The assumptions made about the future that guide PPBE lead to the creation of resources that elements within the Department of Defense become committed to. When those assumptions conflict with reality, it is only natural that the Pentagon’s bureaucracies will look to consolidate what it planned for, rather than seek new—or more cost effective—ways to address its new reality.