Old Rabbit has a good point. I own two horses, one of them a former race horse. He loves to work, be it on a lunge line or under saddle. If you start tacking up another horse he cries until you take him out and tack him up too. And it's not just attention he's after. Even if your petting and brushing him, he'd rather be working.
As for the other, he's much the same. Though he has less desire to work he still enjoys it and loves learning new things more than anything else. As a three year old after being green broke for three months (and not ridden much during then) we took him on a trail ride just to see how he would do. He was alone, in a place he had never been before doing something he hadn't done before, yet he acted like he had been riding trails his whole life. He just did it because that's what made us happy, and he trusted us and enjoyed exploring.