Decades of psychological wisdom have established contact with reality as a hallmark of mental health. The well-adjusted person engages in accurate reality testing, whereas the individual whose vision is clouded by illusion is regarded as vulnerable to mental illness.
Certain illusions are adaptive for mental health and well-being. Unrealistically positive self-evaluations, unrealistic optimism and an exaggerated sense of control or mastery are part of normal thinking. The only people who tend to see themselves as other see them are moderately depressed, low in self-esteem, or both. Positive illusions help make each individual's world a warmer and more active and beneficent place in which to live.