Though while I do think the idea of "secure attachment" does play a large role in future "well-being" I think this theory fails to incorporate other factors such as heredity and environment. For example, siblings in a family may have all had "secure attachment", but not all of them may not have future "well-being". This because they each had different environments and genetic traits.
I agree that another variable could be heredity. I think your example of siblings with different genes is a good example, as not all children in a family are equally securely attached or show the same degree of adjustment later in life.
