The identification of policy as a set or web of decisions is useful in that it underlines the notion that policy is best seen as a course of action—or inaction—rather than a single, discrete decision or action. The policy process is sometimes characterized as a "black box" which converts inputs into outputs. Empirical studies of policies in the real world sometimes cast doubt on the idea that policy can usefully be understood solely as plan or design, and instead draw attention to policy as practice. The discipline of policy analysis has grown up around this complexity, containing competing schools of thought and offering differing definitions. A policy must be distinguished from a decision. The policy formulation process might be so intensely political as to render the prospect of coherence improbable. Policies might fail to achieve their objectives, or even have results opposite to those intended.