In an ideal world, ballistic missile defense designs and acquisition decisions are driven by realistic threat assessments and threat models, and the modeling uncertainty is incorporated in design trades. In reality, other factors can influence acquisition, and these factors can create pressure to tailor the threat to suit the currently feasible design; in effect, the acquisition environment partially drives the threat assessment. For example, factors like political agendas, technology development, or infrastructure sustainment may argue for missile defense system development. Ballistic missile threat models are most susceptible to this influence when the threat is ambiguous or has yet to appear; in that case, threat projections may be advanced by those with the most policy influence. Those top-level threats have tended toward the conservative, or most threatening, end of the spectrum. In the context of long-range missiles, the odds can favor the offense, particularly for a technologically advanced and responsive adversary, which can discourage the development and deployment of a missile defense. Nevertheless, there may be good reasons for pursuing a missile defense regardless of the odds. However, the threat description should be insulated from external factors and be as realistic as possible to preclude poor defense system design decisions that might limit future enhancements needed to handle an emerging threat.