The Id is the source of instinctual drive which follows pleasure principle. These drives are of two opposite types ; (1) Life instinct : It is a constructive drive of a sexual nature which constitutes the libido or Eros the basic energy of life.
(2) Death instinct : It is a destructive drive and tends towards aggression, destruction etc. There are two directions of aggression - External and Internal. When external aggression is extreme, the behaviour like biting, murder, quarreling and harm to others can be seen. While in internal aggression, the person harms himself by nail biting, peeling the skin from the fingers or committing suicide in extreme situation.