I have often wondered if some race horses have an attitude like DiDi. The fans study a horse's lineage and training plan and jockey while failing to realize before they bet their money that the horse might not "feel like it" today. I am sure horses have different priorities and just because we think Derby day is a good day to run fast doesn't mean they see it the same way.
Dick Francis is famous now as a mystery writer, but his autobiography (http://www.amazon.com/Sport-Queens-Autobiography-Dick-Francis/dp/0330339028/ref=sr_1_1?ie=UTF8&qid=1297190626&sr=8-1) covers his days as a steeplechase jockey. He mentions several horses he rode that would race their hearts our one day, and just not care the next. He said the fans would blame the jockey, but the reality is that no jockey can do anything to make a horse run competitively. They can guide it, or encourage it, but the desire to win has to come from within the horse, and some horses aren't consistent in their desire.
My own mare will never win anything. Certainly not with me on her back! But there are days, many of them, where she'll try very hard to make our ride a success. And there are days like yesterday, where she technically did everything I asked of her, but with resentment and contempt coming from every pore. It really seems like sarcasm to me - "Why yes, I'm doing EXACTLY what you ask...isn't this FUN! What? YOU aren't having fun? Well I am...can't you feel how much fun I'm having, you idiot!"
It isn't feed, or hormones, it is attitude. And sometimes I can try again a couple of hours later, and she'll be all sunshine. Or not. She is usually obedient, but she is ALWAYS an independent mind.
I think that is why I'm enjoying the posts on Didi. My horse doesn't have great breeding, fine training or a competent rider, but she is a diva thru and thru. And it is nice to know that I'm not alone, and that even well bred and well trained horses can sometimes be...well, divas.