gratitude
She learnt, at a very early age, that it was important to show gratitude for gifts received, and to respond in whatever way the giver was likely to expect. So she'd gush for one aunt, smile shyly for another, but always make sure the item stayed in sight (year after year), so it would look like she used it and really appreciated it, even if in fact she couldn't stand the sight of it.
Years later she would try to explain to a series of psychiatrists that she was happy to take responsibility for herself, truly, but it was her parents' fault she was a hoarder. She had learned too well, see, and could remember exactly who gave her what, if not always precisely when, and on attempting to divest herself of excess posessions would break out into a sweat, because it was perfectly plain that the moment she got rid of whichever item, the giver would drop in unannounced, and she would be left blushing and stammering as to what had happened to that lovely little whatever-it-was she'd received that birthday past.
The older she gets the more of a problem it is. Please, she tells everyone, No presents, no more presents, please! Because she's got nowhere to put anything, and can't get rid of anything, and there's nothing much that she needs or wants anyway. They pay no attention, of course. So it's a pair of earrings that are not even remotely "her", from someone she adores, and she gushes and shows her gratitude because she doesn't want to hurt her friend's feelings. Then there's a pretty glass trinket box from an old friend, and it does happen to have her favourite colour incorporated in the design, so she can muster just a little genuine enthusiasm, but she's never been a trinket box kinda girl. Oh, and the boyfriend has given her another cuddly toy, which is nice, because she likes those, but she feels guilty looking at it, because it's just a wee bit too cartoonish, and not much like anything she would have chosen for herself.
She wouldn't dream of hurting anyone's feelings, so everything has to be kept, even if it's been a quarter century since receipt, and the giver has surely forgotten all about it by now. It's almost like turning into her mother (for whom the only welcome presents are those that can be used up, like soap), and she feels there's some kind of irony in that, but can't quite put her finger on it.