There's a concept in psychiatry that most of us don't consider often. Insight, defined in my intro to clinical psychiatry book as, "the patient's awareness of his or her mental illness and the ability to connect this disturbance to other problems", is not really the most important important aspect of a patient's mental state from a diagnostic perspective.
But what strikes me is that insight is perhaps the most important factor in determining our emotional reaction to the patient. Consider an older patient with dementia, for example. He is losing his mind, forgetting who his children are, giving them gruff and slightly wary welcomes when they come to visit. Maybe we roll our eyes, shake our heads a little as we repeat what we've been telling him for weeks, that his visitors are his family, and he should be nice and sit and talk with them for awhile.
Now consider the same patient, who, in a moment of insight, realizes that his mind is slipping away past his reach. A lifetime of professional accomplishments and personal connections is blurring into an oblivion that he recognizes as the path towards the end. Our patient has now gone from a sweet old nuisance to a tragedy.
Why? What is it about this one feature that evokes such a an empathetic response? I think it's because insight gets at what makes us human. Ants will never have the insight into their situation aside from an instinct to run when they see large objects moving quickly near them. Insight implies a broader realization, a conceptual understanding of illness and one's relationship to it.
Ancient playwrights knew that insight is the stuff tragedy is made of: the entire, horrible events that lead to Oedipus's putting his eyes out happen before the play starts. Things only turn tragic when Oedipus realizes what has occurred -- when he gains insight.
Although embedded within the endless descriptive terminology that psychiatry uses, insight describes more than a symptom of an illness. It describes an expression of humanity.