Well, I do acknowledge that those memories of a time more secure, carefree and 'happy' (in short) does make one smile from time to time knowing that they had been lucky enough to actually HAVE those memories. I guess that may very likely be the reason for people to re-visit or even fall back on their old memories whenever they get dis-satisfied with the way their lives are headed and maybe due to the lack of control they have over the course of their lives. Thus, the sense of longing surfaces ... but! It is indeed rather frustrating to know that the REAL appreciation of what you once had only comes about by its loss. :(
I guess that 'longing' for a past memory's circumstance is what drives many people to do irrational things to try to put everything together, the way it was in the past. The worst thing is that, in that state, no one really realizes the uselessness of longing for things to be the way they were in the past as well, the present remains the same. Desperation at its strongest? I think so. But for what?
I think the answer would be this: A false sense of security, as needed by the individual (but not acknowledged), for them to carry on in their current lives until they reach another peak of happiness in their lives. Haha. Maybe. Or as a form of consolation?
At least I have my happy memories left if I have nothing else! Haha. :D