From various studies mentioned in the text book, and even from the descriptions of different attachments, it seems sensible that there is correlation between attachment as infants and their future well-being. While it may be true that it is likely that an infant who developed secure attachment will have better social characteristics, there is still room for exceptions.
For example, the book mentions that sensitive mother leads to secure attachment, which leads to future well being of the infant. Then what creates sensitive mother? In other words, in what type of environment do sensitive mothers live in? Would it be easy for single mothers to be sensitive to their babies all the time? What about single mothers? Or mothers abused by their husbands, or abusing alcohol and/or drugs? I am not trying to say single mothers or working mothers are ALWAYS insensitive or bad in anyways, but do you see the point Im getting at? We could make an assumption that sensitive mothers usually mean a household that is suitable or raising children. If this assumption is safe to make, then it may as well be that the environment the children grow up in effects their future social characteristics.
(If I sounded biased, judgmental, and/or insensitive, please understand I did not mean to.)