Know how to assess people including yourself, with the objective of understanding their preferences, strengths and weaknesses.
Although people can be very different it is possible to begin to assess people by establishing a category within which they fit. Also do this for yourself because this will help you to see why you may not be a typical member of a category and therefore other people may not be typical either. Categories of assessment should be taken as a guide rather then an answer.
The knowledge named 'Assessing People' is considered to be rather important.
In addition, the knowledge is thought to be rather complex and difficult to learn, it is almost always learned from experience, and is mostly specialised knowledge.
Opinion is that it is fairly justifiable knowledge.