text: Paranoid definition: Exhibiting or characterized by extreme and irrational fear or distrust of others \n\nPessimistic definition: A tendency to stress the negative or unfavorable or to take the gloomiest possible view\n\nIt is not wrong to have such characcteristics, its just that it is negative and not healthy to have them, and they affect your life. A paranoid person would over-react to things that s/he is afraid of or have negative thoughts of. Say for example, a paranoid old lady hears a knock on the door, she thinks its a man trying to harm her that she carries a knife when opening the door, when actually, the man is a delivery boy.\n\nBeing pessimistic on the other hand, also affects a person's life. If that person keeps on thinking negatively, he will not be able to go forward or succeed in life. For example, a group of student participates in a competition against an opponent group which has a higher opportunity to win them; if the group of students feel intimidated by their better opponent and they think negatively, they will lose their fighting spirit and have no motivation to do their best to win the opponent.