Really interesting concept. "People with a strong ability to mentalize have the often difficult-to-attain perspective of understanding themselves from the outside and others from the inside".
Understanding themselves from the outside and the others from the inside. In a way it puts the critical emphasis back to the early years and education, about values.
How much value placed on relationships and self improvement, some people don't need much self improvement at all, because are born naturally well adjusted to social interactions. Their natural traits are rewarded with lots of good friends, they then go on to master many types of social interactions and they know how to have fun.
They don't need to do much analysis and understanding of others mind on the "inside", they just play and create the social atmosphere that others will go along with and respond to according to their moods. Over obsessive work goals can treat on others toes, and be socially ejected. Personal ambitions can also be damaging to relationships.