Why is psychology an important theme in The Crying of Lot 49?

In the story The Crying of Lot 49, the main character, Oedipa’s psychological state is brought into question when she enters a quest to understand the defunct postal system, Trystero. Her former lover leaves his estate and belongings to her when he dies. She discovers stamps that were part of Trystero. She travels Southern California to determine if the system is still in existence. She comes to believes that the mailboxes are still functioning and are W.A.S.T.E. (We Await Silent Tristero’s Empire) bins. The more clues she gathers the more it begins to seem that she is making up references in her own head. The reader begins to question her credibility. She becomes paranoid, seeing the clues everywhere she goes. She cannot tell fact from fiction and believes Trystero to be real or the fictitious musings of her ex-lover. Throughout the story Oedipa comes across several characters with various forms of psychosis. One character attends Inamorati Anonymous a group dedicated to avoid falling in love. Another is a former SS agent who is currently a therapist.