I believe that some of the correlation can be explained by personality factors - not how one interacts and forms attachments, but one's general demeanor and attitude in the absence of company. Someone who feels confident about themselves will most often be friendly, embrace intimacy, and consider their relationships to be strong and healthy. At a young age, this is recognized as secure attachment; later, the people with this attachment also report better wellbeing. There is certainly a correlation, but we could attribute this to the fact that they still have the same mentality - a positive outlook; one's success or happiness may not be based on one's attachment style with others, but one's attachment with the self.
