Questions of personality have vexed mankind from the dawn of personhood: can people change? How do others perceive me? What is the difference between normal and pathological behavior? One's personality is so pervasive and all-important that it presents a clinical paradox of sorts: it is hard to assess our own personality, and impossible to overlook that of others.
Personality disorders are deeply ingrained ways of thinking and behaving that are inflexible and generally lead to impaired relationships with others. Mental health professionals formally recognize 10 disorders that fall into 3 clusters (A, B, and C), although there is now known to be much overlap between the disorders, each of which exists on a spectrum.