They seem to be incapable of it.
In paranoia the symptoms of delusion appear gradually, and the patient is sentimental, suspicious, irritable, introverted, depressed, obstinate, jealous, selfish, unsocial and bitter. Hence his social and family adjustment is not desirable, and while he has the highest desirable, the effort that he is prepared to expend is correspondingly little. Here the person does not acknowledge his own failures or faults, and by sometimes accepting certain qualities as belonging to himself, even when imaginary, he develops paranoia.
The “Diagnostic and Statistical Manual of Mental Disorders”, fourth edition (DSM-IV), the US manual of the mental health professional; lists the following symptoms for paranoid personality disorder:
preoccupied with unsupported doubts about friends or associates
suspicious; unfounded suspicions; believes others are plotting against him/her
perceives attacks on his/her reputation that are not clear to others, and is quick to counterattack
maintains unfounded suspicions regarding the fidelity of a spouse or significant other
reads negative meanings into innocuous remarks
reluctant to confide in others due to a fear that information may be used against him/her
Kinds of paranoia
Persecutory paranoia - This is the most prevalent type of paranoia, and in this patient makes himself believe that all those around him are his enemies, bent on harming him or even taking his life. In this delusion people of an aggressive temperament often turns dangerous killers.
Delusion of Grandeur - In this patient believes himself to be, a great individual, and according to Bleuler, this delusion of grandeur accompanies a persecutory delusion.
Religious paranoia - Here the patients suffer from a permanent delusion of a primarily religious nature. He for example believes, that he is the messenger of God who has been sent to the world to propagate some religion.
Reformatory paranoia - In this the patient turns to considering himself a great reformer. He accordingly looks upon all those around him. As suffering from dangerous disease, and believes that he is their reformer and curator.
Erotic paranoia - Here the patient often tends to believe that some members of the family of the opposite sex, belonging to an illustrious family, want to marry him. Such people even write love letters and there by, cause much botheration to other people.
Litigious paranoia - In this kind the patient takes to feeling meaningless cases against other people and feels that people are linked together to bother him. Sometimes he, even tries to murder.
Hypochondrical paranoia - In this kind the patients believes that he is suffering from all kind of ridiculous diseases, and also that some other people are to blame for his suffering.
Cause of Paranoia
1) Homosexual fixation: According to Freud, the patient suffering from the disease has repressed his tendency to homosexual love to such an extent that he develops a fixation concerning it. Freud’s view has been found correct in many cases, but it does not explain each and every case of the disease.
2) Feelings of inferiority: Here the psychologists have found that the main cause of paranoia is a sense of inferiority that may be caused by a variety of condition such as failure, disgust, sense of guilt.
3) Emotional complex: Certain psychologist points out emotional complexes, and also believe that they are seen to be present in other mental diseases as also in normal individuals.
4) Personality type: Cameron believes a certain type to be more susceptible to this disease, a personality that has sentimentally, jealousy, suspicion, ambition, selfishness and shyness etc. Patients of paranoia do exhibit these peculiarities of personality but on this basis they cannot be said to belong to definite personality.
5) Heredity: In the opinion of Fisher the main responsibility of paranoia lies fairly and squarely upon heredity, although he does not deny the importance of repression and emotional complexes. The causes of paranoia are not physical because no patient exhibits any signs of physical deformity and among the causes there are many important” ones, such as defects of personality, sense of inferiority, repression etc.
http://www.depression-guide.com/paranoia.htm
Remind you of a certain bunch?