I became interested in writing this book approximately ten years ago when, having become established as a psychiatrist, I became increasingly impressed by the vague, capricious and generally unsatisfactory character of the widely used concept of mental illness and its corollaries, diagnosis, prognosis and treatment.
Although (mental illness) might have been a useful concept in the nineteenth century, today it is scientifically worthless and socially harmful.
In non-psychiatric circles mental illness all too often is considered to be whatever psychiatrists say it is. The answer to the question, Who is mentally ill? thus becomes: Those who are confined in mental hospitals or who consult psychiatrists in their private offices.

Preface to the First Edition. - The Myth of Mental Illness: Foundations of a Theory of Personal Conduct (1974)