What term describes the phenomenon when an individual’s skills have decreased to the point that they cannot function effectively in a specific area?

The phenomenon described in the question reflects a situation where an individual's abilities have diminished to the extent that they struggle to function effectively in a particular area, which is best captured by the term "skill regression." Skill regression refers to a decline or loss of skills that were previously developed, resulting in reduced performance or competency.

Compensation, while it suggests a method of coping with deficiencies in one area by enhancing abilities in another, does not directly address the decline in capability itself. Cognitive decline generally refers to a broader deterioration of cognitive functions, such as memory and attention, rather than specifically highlighting the loss of skills relevant to a task or activity. Detrimental adjustment lacks specificity in describing the processes that occur when an individual's skills drop below effective functioning and does not resonate as closely with the context of skill degradation.

Overall, skill regression captures the essence of the scenario presented, emphasizing the individual's inability to maintain competence in a specific area due to the decline in their abilities.