Gambling is a game of extreme excitement and tension.  Suppose you bet on a football match and at the last moment you are at the moment of defeat, if you think about how your mental and nervous pressure will be, you will find the answer to this question easily.
I always feel nervous in gambling and investing and I can't control my excitement until I win a bet. But this excited state is not easy to control but many times over excited state is responsible for psychological damage as well as losses in gambling.