" Clinicians and researchers have remarked that where the higher emotions are concerned, sociopaths can “know the words but not the music.” They must learn to appear emotional as you and I would learn a second language, which is to say, by observation, imitation, and practice. And just as you or I, with practice, might become fluent in another language, so an intelligent sociopath may become convincingly fluent in “conversational emotion.” In fact, this would seem to be only a mildly challenging intellectual task, quite a lot easier than learning French or Chinese. Any person who can observe human actions even superficially, or who can read novels and watch old movies, can learn to act romantic or interested or softhearted. Virtually anyone can learn to say “I love you,” or to appear smitten and say the words, “Oh my! What a cute little puppy!” But not all human beings are capable of experiencing the emotion implied by the behavior. Sociopaths never do. "

― Martha Stout , The Sociopath Next Door