As important component of game theory is the notion of deterrence. Deterrence is the effort to prevent an opponent from undertaking an action by inspiring fear of the consequences of the action. Players engage in deterrence when they threaten their opponents with retaliatory actions that promise to impose cost on their opponents that are far in-excess of any benefits their opponents might envision by taking these actions. Deterrence is really a psychological defense : it tries to prevent opponents from undertaking a particular action by creating in their minds the fear of costly retaliation.