It's also worth noting that PDs tend to be pervasive in that they both effect every part of a person's life AND most people suffering from a PD tend not to recognize the problem itself; that is, they may instead see everyone else's perspective as the odd one. A quality that seems to appear in each PD over and over again is a difference in perception. This difference in perception is so pervasive that it is often extremely difficult for the person with a PD to understand that others see the world differently. This makes PDs extremely difficult to treat as the symptoms are mostly felt by other people who interact with the IP!