It is totally normal to express emotions and feel disappointed, happy and etc when doing something. Moreover, I can say that there are people who feel disappointed also when they win. How about that? Its either greed and feeling that it is always not enough, or people got so into gambling, spend so much time in it, that they find it hard to be happy. Of course I also feel disappointed when expected outcome did not come, but I understand that that is gambling, and it is normal to lose or get random outcomes.