Impairment evaluations often occur within an adversarial context that involves a claimant or plaintiff vs a defense or benefits system; this adversarial context may precipitate proposals for observations of a clinical evaluation (eg, by an attorney or attorneys for one or both parties, a court reporter, a clinical expert, other consultant; audio or video also may be recorded). Evaluators, judges, and state workers’ compensation systems sometimes allow such observation, but a century of scientific research has reliably demonstrated that any observation changes an examinee's presentation in ways that are not themselves predictable. Such contamination leaves the evaluation results without a scientifically credible analysis, rendering observed evaluations futile exercises at best and sources of misinformation at worst. This article reviews the research in social psychology regarding “social facilitation and inhibition,” which has identified an extensive list of factors that are affected by observation (eg, complexity or novelty of the issue being evaluated, perceptions of the observer as an evaluator, stranger, or ally, number of observers, and other factors). No mechanism allows an evaluator to systematically account for the effects of all such variables for any given evaluation. When observation is mandatory, the evaluator should clearly document and communicate that a credible direct evaluation was rendered impossible, to the detriment of the referring party and the system as a whole.