It could be possible that the third factor that would influence both type of attachment and well-being later in life is something genetic, let's say a certain gene that causes both of these. This stays in line with the theory that type of attachment and well-being later in life are both effects of a different cause. This cause could be something genetic that reveals itself in let's say temperment, or it could also be something genetic that doesn't reveal itself other than type of attachment and well-being later in life at all.
