Paranoia is defined as a psychological "symptom." A person who is paranoid "feels as if the world is 'out to get' him or her." Because of this underlying feeling, persons suffering from paranoia regard the people around them, if not all humanity, with suspicion.
Paranoia may lead to persons having great difficulty relating to other people because the paranoid person is constantly on guard, waiting for the other person to betray him/her in some way. Persons who are paranoid may accuse others of plotting against them and end up alienating the others instead of building positive relationships.