Psychiatrists have been using the concept of psychiatric disorders since the 1990s. A mental disorder refers to a clinically identifiable set of psychiatric symptoms or behaviors (e.g., depression, anxiety, hallucinations, delusions, or excessive drinking behavior, etc.) that in most cases are associated with distress and/or impair personal functioning. The etiology may be physical or psychological or a combination of both. The presence of only isolated psychobehavioral symptoms that do not cause mental distress or impair the functioning of the individual cannot be called a mental disorder. For example, if a person is very afraid of rats, but rarely encounters rats when living or working in the city, and the fear of rats does not cause significant mental distress or impairment, the person cannot be said to have a mental disorder. Imagine that the person changes to an environment where rats are often encountered, or even sees live rats running or dead rats on the paths. She/he would be afraid to go out, work in the fields or do other things, which would be consistent with the diagnosis of mental disorder. There are symptoms – excessive fear of rats; mental suffering – fear and tension all day long; functional impairment – difficulty in performing daily tasks. Thus the various elements for the diagnosis of mental disorder are present.