Final answer:
The definition of 'failure to function adequately' as a measure of abnormality is problematic because it does not take into account cultural diversity, possibly leading to the misdiagnosis of culturally normative behaviors as pathological.
Step-by-step explanation:
One issue with "failure to function adequately" as a definition of abnormality is that it fails to account for cultural diversity. This criterion for diagnosing mental illnesses might overlook the fact that what is considered to be functional can vary greatly between different cultures. The concept of cultural concepts of distress (CCD) highlights how mental illness can manifest differently across cultures, which the "failure to function adequately" definition may not accommodate. Additionally, this definition could pathologize behaviors that are culturally normative simply because they do not align with the observer's understanding of functionality.