One factor that can influence a child's attachment early in life is the family's stability and presence of both parents continually throughout a child's life. The more constant the relationships in early life, the more important relationships will be to the person later in life. They will also expect and know how to foster meaningful, long-term relationships because they grew up in an environment where these types of relationships were present and were fostered. Thus, attachement style does not cause the ability to form better relationships later in life, but rather the things that influence secure attachment also influence relationships with all people.
I definitely agree with this. With a stable base and good example to look to, children are provided with a good foundation for their growth in the future.