Mental and bodily expressions of human behaviours spring from decisions made by humans and based upon perceptual thinking processes. The human thinking processes form the basis of cognition and at times cognitive distortions happen. Such occurrences result in dysfunctional unrealistic thoughts that arise from systematic bias in the way we think about reality.

Albert Ellis (1994a) proposed three mental processes that interfere with their healthy function. They are:

1. Being critical of oneself for performing poorly or being rejected
2. Being unkind to and critical of others for performing poorly
3. Blaming everyone and everything for "poor, dislikable condition".

Aaron Beck (1976) proposed five common mental dysfunction which he termed as cognitive distortions. They are:

1. Expressing thoughts in "black or white" thinking - the two extremes.
2. Magnifying the negative aspects of something which filters out the positive.
3. Thinking you know exactly what other people are thinking, particularly if it relates to you.
4. Thinking that your worst nightmare will come true and that it will be intolerable.
5. Believe either that you are helpless and totally subjected to forces beyond your control or that you must rightly control your life for fear that if you don't, you will never be able to regain control.

The goal of cognitive and behavioural therapy is to correct and change those dysfunctional, unrealistic thoughts to realistic ones and to make client aware of the relationship between thoughts, feelings and behaviour.