资料题：Why did Joan feel sorry for herself（　）。

Joan was a nurse who worked in a children's hospital.One evening there was a big dance atthe hospital.Most of the doctors and nurses would be there, but of course some had to be left tolook after the children, and Joan was not one of the lucky ones who were free to go to the dance.She liked dancing very much, so when she had to start work that evening while her friends were getting ready to go to the dance, she felt very sorry for herself.She went to each sick child one after another and said good night, until she came to one little boy whom she very fond of.His name was Dick, and he was eleven years old, but he already talked like an adult.Poor Dick had a very serious illness, and now he Was hardly able to move any part of his body except his hands.Joan knew that he would never get any better, but he was always happy and always thinking about other people instead of about himself.He knew that Joan loved dancing, so now, when she came to say goodnight to him, he greeted her with the words," I'm very sorry that you have to miss the dance because of us.But we're going to have a party for you.If you look in my drawer, you'll find a piece of cake.I saved it from my supper today, so its quite fresh.And there's also a shilling there, which my mother gave me last week.You can buy something to drink with that.And I'd get up and dance with you myself if I was able to," he added.Suddenly the hospital dance seemed very far away and not at all important to Joan.