Failure to function means those outside the individual do not have to label a person as mentally abnormal which still carries stigma in many societies. Unlike the deviation of social norms focusing on public view, it recognizes a persons subjective experience as a means of helping to define who is abnormal. We can focusing on treating the behaviour that is hindering the person from leading an adequately normal life and offer treatment to encourage more adaptive behaviour. However, it is not without its problems. The first limitation is that apparently abnormal behaviour may actually be helpful, functional and adaptive for the individual.
For example, those with obsessive-compulsive disorders find that their obsessions (some maybe socially acceptable behaviour such as hand-washing) make them feel happy. The second limitation is some of its criteria depend on subjective judgements of other people. It may be that someone is deemed abnormal simply because the observer experiences discomfort in watching their behaviour and in their own mind believes them unable to function adequately. Thirdly, abnormality can be defined as the deviation from ideal mental health.