Military doctrine, strategy and tactics are usually honed over the course of years, and carefully decided by experts. Developing a successful doctrine and strategy takes years of effort and time, and having a coherent doctrine to work from makes managing and running an Army a whole lot easier. In other words, you need to spend years to develop a successful doctrine and strategy, countless man hours, and a vast sum of money and effort… Just to lose in two World Wars or struggle against peasant farmers.
… The German General Staff (formed out of the Prussian General Staff) and the United States Military after World War II both spent huge sums of money, manpower and time studying all aspects of war. The German General Staff came up with ideas like the Schlieffen Plan and the US Military came up with a vast number of plans and contingencies for almost any situation (look for a future article detailing US War Department planning in the 1920’s and 1930’s).
Interesting line of thinking by General Eisenhower. Taking the legwork to actually do the planning is difficult; only writing up a plan and expecting people to execute your plan is easy (and lazy).
Military Planning boils down to a specific plan for a specific place and operation. It is not an all encompassing framework or checklist of things to do, but instead a general plan of how to achieve a desired end state. Doctrine is a bit more complicated (for an excellent read on what exactly is doctrine, check this out Modern War Article on Doctrine). Doctrine is essentially a guideline and framework for how a unit functions, a common language for units to communicate terms, and the principles and tactics an Army uses to fight.
Doctrine and Planning are necessary for any military unit or function, but they are not the solution. The Schlieffen Plan did not pan out too well for the Germans (they ended up getting bogged down in Belgium and France and were not able to march successfully on Paris). For American military planners, the design of attrition warfare in Vietnam and not implementing a full-on counter insurgency doctrine until the late 2000’s show a few instances of planning and doctrine coming up short.