Unable to say goodbye

I found this interesting:

". . . a basic problem of insecurely attached individuals is that they have been unable to say goodbye to 'lost' attachment figures; that is, they have been unable to forgive, forget, and reconcile themselves to the reality of unsuccessful past attachments"

--p. 336, "Insecure Attachment in Personality Disorders" by Malcolm West and Adrienne Keller, in Attachment in Adults: Clinical and Developmental Perspectives edited by Michael B. Sperling and William H. Berman)

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I suppose I just think it's well put--  I can see that I have spent almost 30 years of my life unable to forgive, forget and reconcile myself to the reality of unsuccessful past attachments, one after another. (I think the "forget" part is idiomatic-- forgive and forget-- not literally forget). I wonder what allows some people to reconcile themselves to reality and others really can't, at least not for certain sometimes quite long stages of life.