Studies have shown that people who tend to have one type of attachment also tend to have higher well-being later in life. However this does not mean that a child's pattern of early attachment causes his/her later adjustment, and claims about attachment causing well-being cannot be made. This is because there are many other factors that needs to be taken into consideration. Personally, I think that the physical and emotional health of the child plays a very important role in their development: i.e. whether the child grows up in a stable environment where he/she is provided and cared for. Factors like these definitely influence the child's later adjustment in some way or another.
I agree that there are many other factors that affect the later adjustment of people and the cause of later adjustment should not be limited to only the type of attachment a person had as a child. There's definitely somewhat of a correlation between early attachment and later adjustment, but there are also other things that affect later adjustment.
