Maybe it was my post you were reading? I am the daughter of a narcissist; I do have narcissistic tendencies myself but without really being narcissistically impaired and yeah, I've got the biographical memory of a money plant. I meet former schoolmates and not only I don't recognize them: I am not even aware they were in my life. When I lived in my native town, I bumped once or twice into complete strangers that revealed to my astonished face they were ex boyfriends of mine

. What I do remember, it's completely devoid of emotion, lacking in detail and sometimes reconstructed in hindsight.
I do have a very good short term memory tho; when I am in a relationship, until it ends, I remember every single moment, every single conversation into the tiniest detail. Then, after some time it has ended, I forget everything: it's like trashing a folder on my pc. I study with ease, data just stick to my brain like glitter on a synthetic jumper, just to be brushed away if it stops being useful (e.g. I used to be fluent in a lesser-known language - now that it's no longer relevant to me, I have a hard time even reading it).
I can say my brain travels light. Each year pushes away the previous one: no memory, I don't get old (until recently, I didn't even get adult

). Why? I am not sure. But I do remember that, at the onset of puberty, I happened to be horribly ashamed by something I had done or had happened to me (obviously I don't remember what) and feeling I couldn't live with the memory of my failure, which obsessed me to the point of paralysis, and that I prayed to forget. Maybe my wish has been granted beyond my wildest dreams - for sure failures don't linger in my head anymore, neither successes do. Maybe it's a defence turned habit. But I wouldn't say that I don't remember because it's not about me, quite the other way round - the more it's about me, the more I forget...
My last squeeze, who has a similar psychological makeover, laments the same selective lack of memory; but in his opinion it's because his life is lived in an emotional haze of confusion in the first place. I don't think I can say the same for myself (but I am not sure either).