The first part of this two-part series discusses psychological influences in delayed and failed recovery and resulting unnecessary work disability; the second part discusses theoretical and practical aspects of the issue, including evaluation and treatment. Delayed and failed recovery and unnecessary disability (DFRUD) refers to a lag in, or lack of, expected recovery from a medical condition and/or unnecessary resultant disability. Causation is complex, and we are not doing well at managing this group of workers using a biomedical model. The traditional biomedical model posits that disease or injury produces symptoms and signs that cause impairment and result in disability. This approach too strictly separates mental phenomena and bodily function (Cartesian dualism) and leads to scientific reductionism when actually six domains are active in worker disability: medical, personal, psychological, sociocultural, systematic (including compensation and insurance), and workplace elements. Medically unexplained physical symptoms (MUPS) should be understood as a disturbance of normal neurological and/or psychological processes underlying symptom production, perception, and experience and cannot be better explained by another physical or psychiatric illness. Within this system of evaluation, administrative and medical iatrogenicity are associated with unnecessary medical care and poor outcomes for individuals. In addition to determining industrial causality and apportionment, if evaluators accept some psychological factors, MUPS, and central sensitization, they must explain to what extent these are compensable. Part two of this article will discuss theoretical and practical approaches, including specific evaluation and treatment methods.