: loss of memory of yarn amount, due usually to yarn stash shock, color fatigue, repression
: a gap in one's memory of his or her stash of yarn
: the selective overlooking or ignoring of events or acts that are not favorable or useful to one's purpose or position; e.g. - "I really thought I had six skeins, not four, of this yarn. Wait, is this sport weight, not worsted? Darn. My stashnesia is getting really out of control."
(Pro tip: an electronic record of stash on Ravelry only helps if you update it.)