From day to day with different people, and over time with the same people, most individuals feel and act pretty consistently. This fundamental fact was discussed in detail (and debated, to some extent) in Chapter 4. Predictability makes it possible to deal with others in a reasonable way, and gives each of us a sense of individual identity. But some people are less consistent than others, and have thoughts, emotions, and behaviors that are in flux and unpredictable even to them. When this pattern becomes extreme, a person may be diagnosed with borderline personality disorder, which is the most severe one on the list. It is characterized by unstable and confused behavior, a poor sense of identity, and patterns of self-harm that range from self-defeating behaviors to self-mutilation to suicide. Their chaotic thoughts, emotions, and behaviors make persons suffering from this disorder very difficult for others to "read"—they would be considered very low on the dimension of judgability considered in Chapter 5 (Flury, Ickes, &amp; Schweinle, 2008).

Borderline personality disorder (BPD) entails so many problems for the affected person that nobody doubts that it is, at the very least, on the "borderline" with severe psychopathology (some writers claim that this is why it's called "borderline," because it lies between the less serious neuroses and the more serious psychoses, but the actual origin of the term is obscure). Its hallmark is emotional instability. The person's mood can change rapidly from one moment to the next, and he may seem on the verge of going to pieces (Gunderson, 1984). The foundation of the disorder, according to some writers, is a sort of "emotional hemophilia," in which a reaction, once stimulated, cannot be stanched-the individual emotionally "bleeds to death" (Kreisman &amp; Straus, 1989, p. 8). Another prominent researcher writes that an individual with this disorder is "the psychological equivalent of [a] third-degree burn patient [with]... no emotional skin. Even the slightest touch or movement can cause immense suffering" (Linehan, 1993, p. 69).

According to the DSM-5, suicide attempts are common among people with BPD, and eventually 8 percent to 10 percent do kill themselves (American Psychiatric Association, 2013, p. 664). If this statistic is even close to correct, then BPD is a dangerous affliction indeed, comparable to the most threatening physical diseases. Even among nonsuicidal people with BPD, self-mutilation is common and may include compulsively "cutting" (with fingernails or knives) (I put this word in quotes because it's almost a technical term; tell a clinical psychologist that someone is "cutting" (or is a "cutter"), and he or she will immediately understand what you are talking about) parts of the body, including the hands, arms, and even genitals. The reasons for this behavior are far from clear; possibilities range from the rather psychoanalytic-sounding speculation that people with BPD feel guilty and are punishing themselves, to the idea that they are so emotionally disconnected that they must hurt themselves to know they are alive. Perhaps the most plausible explanation comes from the description of the inner life of persons with this disorder as characterized by "emotional cascades," which are "vicious cycles of intense rumination and negative affect" that lead to extreme suffering (Selby, Anestis, Bender, &amp; Joiner, 2009, p. 375). Behaviors such as using fingernail clippers to pull off slices of skin (Cloud, 2008) may interrupt the process (these authors suggest—seriously—that teaching these patients other means of distraction, such as Sudoku, might be helpful.). Several studies support the conclusion that the main reason people engage in gruesome self-harm is "to alleviate negative emotions" (Klonsky, 2011, p. 1981; see also Klonsky &amp; Mühlenkamp, 2007). Consider what this means: The feelings people with BPD are seeking to avoid must hurt even worse.

Many people with BPD literally do not know who they are. They may have great difficulty understanding how they appear to others, and be confused about their values, career goals, and even sexual identity. They do not understand their own actions—cutters, for example, can say almost nothing meaningful about why they do it—and those with BPD may try to be social chameleons, avoiding behavioral choices and fading into the background by doing what everybody else seems to be doing. Recall from Chapter 16 that one function of the self is to provide a marker on an internal map that says "you are here." People with BPD have lost the map.

The interpersonal relationships of people with BPD are confusing, chaotic, noisy, unpredictable, and unstable. In part, this is because they are prone to splitting, a term you may recall from object relations theory (described in Chapter 11) that refers to the tendency to view other people as either all good or all bad. Thus, a new relationship may be perceived as perfect, the best ever. Then, the first disappointment leads the person to conclude that the new partner is hopelessly thoughtless and cruel. These two extreme views, as Freud would have noted, have the same underlying dynamic. In both cases, the person with BPD is unable to handle the complex reality that people have a mix of good and bad characteristics, so she oversimplifies by jumping to one extreme evaluation or the other.

All of the personality disorders are rather mixed bags of indicators, and BPD be the most mixed of all. It is difficult to find a coherent, common may thread among its characteristics, which may be why the label "borderline" is so descriptively unhelpful. Some psychologists, indeed, have suggested that this category is too diffuse and should be abandoned. But although other disorders were eliminated in the new system in the DSM-5, as we have seen, this one remains. The confusing and mixed-up nature of BPD may be the whole point. The pattern of emotion and behavior of someone with this disorder is sto have no pattern. The personality itself is confused and disorganized, and the results can be disastrous and even fatal.

A huge amount of research attention has been paid to BPD in recent years, and some progress has been made. New theories have been proposed about its origins. One theory is that BPD arises when a genetic risk factor combines with an early family environment that fails to teach children how to understand and regulate their emotions. Children are put at risk when their "expressions of emotion rejected by the family and life's problems are oversimplified" (Crowell, Beauchaine, &amp; Linehan, 2009, p. 504). Another promising suggestion is that the disorder stems from problems with the endogenous opioid system, which regulates the body's natural painkillers (the endorphins described in Chapter 8). "Frantic efforts to avoid abandonment, frequent and risky sexual contacts, and attention-seeking behavior"—all hallmarks of BPD—may be attempts to stimulate this system and thereby feel better (Bandelow, Schmahl, Falkai, &amp; Wedekind, 2010, p. 623).

The most encouraging development is in therapies that might actually help. A technique called dialectical behavioral therapy (Linehan, 1993) teaches skills for emotional self-control. In individual and group sessions, the therapist and client closely examine past episodes of inappropriate emotional reactions and analyze how similar situations could be handled better next time. In a sense, it's basic training in how to deal with emotions-a skill people with this disorder somehow never learned.

The DSM-5 estimates that about 2 percent of the population has this disorder, and about 75 percent of those diagnosed are female.

[This is an excerpt from pages 625-627 of *The Personality Puzzle*, a personality psychology textbook by David C. Funder.]

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As a psychology student learning about personality disorders, I showed this passage to my friend with BPD last year. She said it was incredibly influential to read. It's not your standard "what it is—symptoms—treatment" internet blog post that barely scrapes past the surface of this incredibly complex disorder: it's an illuminating description that provides the most profound insight I've ever read on this disorder.  I hope that reading this can help some of you in some small way.