Dr. Stanley Goldstein - Author and Psychologist

Once, during a routine medical examination, I remarked to the physician that I never had a chronic illness and doubted that I would. "That's a good delusion. Keep it," she advised. Which is true since even the healthiest person can't predict the vagaries of their genetics or fate.
This remembrance entered my mind after speaking with a patient whose delusional belief seemed ego-syntonic, enabling them to work productively though with difficulty in relationships.
A delusion,which is a fixed false balief, can range widely in both the personal and political spheres. Feeling unjustified guilt about their child's autism (which is a vastly misdiagnosed condition), a mother might falsely ascribe it to vaccination or air polution. Similarly, masochistic behavior or anorexia nervosa (which has the highest death rate of all the mental health conditions) may be considered "normal" by its sufferer rather than accurately, as deriving from damaged childhood experiences which can be healed through psychotherapy. And one who attributes their or their nation's problems to a minority population may feel better even if their life situation remains unimproved, as happened in Nazi Germany and today's inhabitants of some nations.
What determines a delusion's benefit or harm depends on its effect: whether or not it enables adequate functioning as a productive member of society without interfering with the rights of others and the maintenance of sound physical health.