Daniel Nettle

“This clarification of the nature of intelligence predicts that there will be no relationship at all between personality and intelligence, but research in the last decade has shown that this is not quite true. There are no very strong relationships between personality and intelligence, but some relationships there are, though debate about their nature and significance goes on. Most strikingly, though, in a couple of studies where relationships between Conscientiousness and intelligence have been found, they are not, as you might imagine, positive, but weakly negative. The smarter people are, the less conscientious they are.13 The most likely explanation for this is that people who are very sharp soon learn that they can get away with not preparing things too much in advance, not being overly disciplined with their time, and so on, since their quick abilities will get them through whatever academic and professional challenges they meet. Conversely, people who are not quite so quick have to use organization and discipline to achieve what some others might achieve carelessly. Thus, a behavioural style is developed that compensates for the level of intelligence, and so ends up inversely related to it. This means that there is no intrinsic genetic connection between low Conscientiousness and high intelligence. Rather, the weak negative correlation is something that emerges through development.”
― Daniel Nettle, Personality: What makes you the way you are

“Obsessive-compulsive personality disorder (OCPD) is unhelpfully named, since it is not particularly closely related to the better known obsessive-compulsive disorder (OCD). It does not tend to co-occur with obsessive-compulsive disorder, or even run in the same families. Obsessive-compulsive disorder is an anxiety disorder, in which the sufferer feels compelled to repeat particular thoughts or actions, such as checking or hand-washing. As an anxious condition, it belongs to the same family as depression and generalized anxiety disorder, and thus is related to high Neuroticism and responds to some extent to serotonergic antidepressant medications. Some people have even seen obsessive-compulsive disorder as a low Conscientiousness problem, since the affected individual cannot inhibit the checking or washing response in rather the same manner as the alcoholic cannot inhibit his desire to drink. Whether this is the right characterization or not, it is clear that OCPD is a very different type of problem.16 What, then, does OCPD entail? Psychiatrists define it as ‘a pervasive pattern of preoccupation with orderliness, perfectionism, and mental and interpersonal control, at the expense of flexibility, openness and efficiency, beginning by early adulthood and present in a variety of contexts’.”
― Daniel Nettle, Personality: What makes you the way you are