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This paper presents a comprehensive discussion on the difficulties of formulating good and stable requirements early in complex engineering programs and the consequences on program execution. Formal classical systems engineering and program management (CSEPM) methodology is based on the assumption that the knowledge to anticipate all interfaces and create good requirements exists early in the program, and that it is a matter of working out the details to build extremely complex devices such as satellites, aircraft, refineries, nuclear power plants, and high-speed rail. The author argues that classical systems engineering and program management works well only for well-understood systems, but it breaks down when the knowledge of what needs to be done still needs to be discovered, which is the case with most complex systems. Once the requirements and interfaces are defined, flowed down, and allocated to all applicable lower levels, the primary mechanism for mission assurance is requirements verification—by test, analysis, inspection, or demonstration. In real programs that develop new systems, the reality leads to the following Faustian choice: Either develop and anticipate all interfaces and requirements early, when the knowledge is not yet available, hoping to make the systems engineering Vee process in one pass and to feed the requirements to numerous suppliers early; or conduct massive, painful, and cost- and schedule-busting requirements changes throughout the program, renegotiating the requirements with the suppliers. This paper traces various historical phases that contribute to the present difficulties with requirements; the author argues that in order to radically change this major deficiency of classical systems engineering and program management, a radical change of the business model is needed, such as that practiced by SpaceX. The paper proposes development of special Lean enablers (LEs) to be formulated for those readers who might be interested in this radical approach. This radical change, though, is just not practical for large engineering programs that have to operate under complex political and financial constraints. The Guide to Lean Enablers for Managing Engineering Programs (Oehmen, 2012) applies to these programs directly. The Lean enablers contain a well-integrated set of systems engineering and program management practices that have the potential to vastly improve the requirements development and related program execution. This paper discusses the applicable Lean enablers.