I've not gotten up that high with knitting, but I can say it is the same with Painting. As you get higher in the aspiration, it takes longer and longer for your sim to actually create those elusive Masterpieces. She made several while getting to that level, then she kept painting excellent ones. I just kept grinding away at it till my sim finally completed that aspiration. She made quite a bit of money during that time, and Plopsy was a great help for that. :)
I told myself it took so long because the Lighting was not right on that particular day, or she was waiting for true inspiration to strike.
